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					Work Site-Based Cancer Prevention:
Primary Results from the
Working Well Trial

Glorian Sorensen, PhD, MPH, Beti Thompson, PhD, Karen Glanz, PhD, MPH,
Ziding Feng, PhD, Susan Kinne, PhD, Carlo DiClemente, PhD, Karen Emmons,
PhD, Jerianne Heimendinger, ScD, MPH, RD, Claudia Probarti, PhD, RD,
and Edward Lichtenstein, PhD, for the Working Well Trial

Introduction                                     This study was conducted in 111 work
                                                 sites by four study centers, a coordinating
     Each year approximately a half-             center, and the National Cancer Institute.
million Americans die from cancer.' It is        The large number of work sites permitted
estimated that up to 70% of these cancers        assessment of change at the work site
are associated with lifestyle or environ-        level. The primary hypothesis of the
mental exposures and are therefore pre-          Working Well Trial was that a sustained
ventable.2 The National Cancer Institute         2-year comprehensive cancer control work
has taken aggressive steps to implement          site health promotion intervention ad-
cancer prevention and control measures           dressing dietary change and smoking
to reduce cancer risk. Among its objec-          cessation, delivered by a participatory
tives are the reduction of average con-          strategy that targeted individuals and the
sumption of fat to 30% of calories or less,      work site environment, would be more
the increase in average consumption of
fiber to 20 g to 30 g per day, the increase in   effective than a minimal intervention in
servings of fruits and vegetables to five or     achieving both individual behavioral and
more per day, and the reduction in the           environmental changes. This paper re-
percentage of adults who smoke to 15%            ports findings on individual behavior
or less.3                                        changes.
     Work sites have been targeted as a
priority location for intervention efforts
aimed at these objectives. They provide
ready access to working populations, the         Glorian Sorensen is with the Dana-Farber
opportunity for promoting environmental          Cancer Institute and the Harvard School of
supports for behavior change, and natural        Public Health, Boston. Beti Thompson, Ziding
structures for social support.45 Few stud-       Feng, and Susan Kinne are with the Fred
ies, however, have employed a random-            Hutchinson Cancer Research Center, Seattle,
                                                 Wash. Karen Glanz is with the Cancer Re-
ized design; often, even those with a            search Center of Hawaii, Honolulu. Carlo
randomized design have compared too              DiClemente is with the University of Houston,
few work sites to have adequate statistical      Tex. Karen Emmons is with Brown University/
power.6 Interventions have typically tar-        The Miriam Hospital, Providence, RI. Jerianne
                                                 Heimendinger is with the National Cancer
geted only the individual, ignoring the          Institute, Rockville, Md. Claudia Probart is
organizational context. Only rarely have         with the Nutrition Department, Penn State
results been based on change in the entire       University, University Park. Edward Lichten-
work site population rather than the             stein is with the Oregon Research Institute,
subset of employees participating in the         Eugene. For a list of the centers and research-
                                                 ers in the Working Well Trial, see the
program.7-9 The study reported here was          Acknowledgments.
designed to address many of these meth-                 Requests for reprints should be sent to
odological problems.                             Glorian Sorensen, PhD, MPH, Dana-Farber
    The purpose of this paper is to              Cancer Institute, Division of Cancer Epidemi-
                                                 ology and Control, 44 Binney St, Boston MA
present the primary outcomes of the              02115.
Working Well Trial, the largest work-site               This paper was accepted November 1,
cancer control trial in the United States.'0      1995.

                                                       American Journal of Public Health 939
Sorensen et aL

Methods                                       represented manufacturing, communica-                The protocol defined core interven-
                                              tions, public service, and utilities. Work     tions directed toward individuals; these
      The Working Well Trial used a           sites ranged in size from 49 to 1700           included a kickoff event, interactive activi-
randomized, matched-pair research de-         workers (mean = 316). As a condition of        ties, posters and brochures, self-assess-
sign, with the work site as the unit of       work-site participation, managers of all       ments, self-help materials, campaigns and
assignment and analysis.10 Because the        work sites agreed on random assignment         contests, and direct education through
work site was the unit of both randomiza-     of their work site to the intervention or      classes and groups. Core interventions
tion and analysis, data from the 111          control group and also agreed to adminis-      aimed at environmental change included
participating work sites were pooled to       ter employee and organizational surveys        consultation on the formation and imple-
test the hypotheses. Cross-sectional sur-     and to deliver the intervention based on       mentation of smoking policy, changes in
veys of individuals and surveys of key        their assignment to group. Although the        food offerings and/or nutrition education
informants were conducted in each work        work sites were a convenience sample and       in cafeterias and vending machines, and
site at baseline and follow-up. After         were recruited by the use of different         catering policies. Additional information
baseline assessments, work sites were         strategies within each study center,'0 a       on the Working Well intervention is
stratified, matched into pairs, and ran-      variety ofwork site environments, types of     provided by Abrams et al.'0
domly assigned within pairs to the inter-     business, and geographic regions was                 Control sites received summary re-
vention or control group. Stratification      represented. As reported previously, there     sults from the employee survey for distri-
factors were the presence of a cafeteria,     were no demographic differences at base-       bution to employees and were asked to
work site size, type of smoking policy,       line or follow-up between intervention         document health promotion activities.
company type, sex distribution, distribu-     and control work sites.11                      Three of the four study centers provided
tion of blue- and white-collar jobs, and                                                     an optional minimal intervention at con-
response rate to the baseline survey.'0       The Working Well Intervention                  trol sites, following a standardized proto-
Evaluation of the effects of the interven-                                                   col that included the distribution of
tion was based on the difference between            The Working Well intervention was        printed materials such as posters and
intervention and control work site means      based on a theoretical model derived           newsletters.
within each work site pair, with adjust-      from individual, organizational, and com-
ment for the baseline work site mean as a     munity activation theories.10 Based on         Data Collection
covariate. Calculations of sample size        these theories, the intervention focused
were based on the differences thought to      on (1) promotion and building awareness,           Data were collected from individual
be important to detect between interven-      (2) action and skills training, and (3)        employees with self-administered surveys
tion and control sites: 2 percentage points   maintenance of behavior and preventing         containing standard items in all study
for the percentage of energy obtained         relapse.'2'13 Participatory strategies fol-    centers. Baseline data were collected
from fat consumption; 3 g of fiber per day    lowed Rothman's community activation           from September to December 1990, and
(1.5 g of fiber per 1000 kilocal); one        principles.14 This literature indicates that   follow-up data, from September to De-
serving of fruits and vegetables per day;     participation in activities is enhanced        cember 1993. Eligible employees were
and a 6-month smoking abstinence rate of      when people are involved in planning and       permanent employees working at least
6%. The power to detect these differences     implementation.15                              50% of the work time. The methods of
was at least 80%. The sample size was               A common intervention protocol           survey distribution varied by study cen-
determined primarily by the smoking           specifying strategies and process objec-       ter." Briefly, Florida and Brown mailed
outcomes, and excess power was there-         tives was implemented in the four study        surveys to each employee in the work site,
fore available for the dietary outcomes. In   centers. The common intervention was           Dana-Farber mailed surveys to a random
addition, analyses were conducted to          targeted at eating patterns in all four        sample of employees in each work site,
examine work-site smoking prevalence.         study centers and smoking in three of the      and MD Anderson administered question-
                                              four study centers. Florida did not include    naires to employees at mandatory work
Description of the Sample                     a smoking intervention, since smoking
                                                                                             site meetings. Follow-up reminders were
                                              was banned at all participating work sites,    sent to maximize response rates. No
     The study was conducted in four                                                         follow-up surveys of nonrespondents were
study centers: the Brown University School    but did target cancer screening practices.     conducted, owing to constraints imposed
of Medicine/Miriam Hospital, the Dana-        The other three sites targeted smoking
                                              and nutrition plus one additional risk
                                                                                             by the work sites.
Farber Cancer Institute/University of
Massachusetts, the University of Florida,     factor (occupational exposures to carcino-
and the MD Anderson Cancer Center.            gens, Dana-Farber; exercise, Brown; and        Pimnary Outcomes
The sample contained 111 work sites that      smokeless tobacco, MD Anderson).                   Nutrition outcomes. The primary
employed over 28 000 workers in 16                  All study centers relied on an inter-    evaluation of dietary change among indi-
states. (As noted in Abrams et al.,'0 114     vention model that used participatory          viduals was based on assessment of
work sites were initially recruited to this   strategies. An employee from each work         nutrient intakes of fat, fiber, and fruits
study. Because of economic dislocations,      site was appointed as the work-site coordi-    and vegetables, using an 88-item semi-
three work sites located at Brown did not     nator and served as the gatekeeper to the      quantitative food-frequency question-
participate in the final survey, leaving a    work site. In addition, employee advisory      naire with portion sizes (176 items to-
total of 111 work sites. Two of these sites   boards were formed as a way to incorpo-        tal).'6"7 This questionnaire was based on
were from the intervention condition, one     rate employee input and concerns. These        the Block food-frequency questionnaire,
from the control. For pairwise analyses,      boards had from 4 to 12 members, who           which has been validated in previous
three pairs were therefore excluded, for a    were trained in the goals and content          studies.'8 The analysis software for the
total of 108 work sites.) The companies       areas of the project.'0                        Working Well food-frequency question-

940 American Journal of Public Health                                                                              July 1996, Vol. 86, No. 7
                                                                                                               Work-Site Cancer Prevention

naire was based on a nutrient database         day, or who defined themselves as current       not used, since there is no theoretical
developed by the University of Minnesota       smokers.                                        approach or literature to justify differen-
Nutrition Coordinating Center.'9 This                                                          tial weighting of particular items.
instrument was pretested prior to use in       Process Evaluation
this study, and minor modifications were             A process evaluation was designed to      StatisticalAnalyses
made to reflect regional dietary differ-       (1) assess the extent to which the interven-          The primary analyses covered 108
ences. The food-frequency questionnaire        tion was delivered, based on data from the      work sites since the 3 work sites not
was selected for use in this study because     "senders" of the intervention (i.e., project    completing the study represented 3 sepa-
it was able to estimate total dietary habits   staff), and (2) assess the extent to which      rate pairs (see "Description ofthe Sample"
and was feasible for such a large-scale,       the intervention was received; using data       under "Methods"). Analyses conducted
population-based study.                        from the "receivers" of the intervention        take into account the work site as the unit
      The outcome variables calculated         (i.e., work-site employees).10 These mea-       of randomization. For continuous vari-
from the food frequency questionnaire          sures were included to assess indepen-          ables (consumption of fat, fiber, and fruits
included the percentage of energy that         dently whether the independent variable         and vegetables at the final employee
came from fat, grams of fiber per 1000         was in fact differentially manipulated          survey), mixed linear models were used,22
kilocalories, and daily servings of fruits     between the intervention and control            where the study center and intervention
and vegetables. The fat and fiber densities    conditions.                                     condition (or treatment arm) were fixed
were chosen as superior to measures of               Assessment of delivery of the interven-   effects, and the pair (or block) and
total grams of fat and fiber because the       tion. To ascertain the extent to which the      treatment-arm-by-block interaction were
densities control for total energy intake.     intervention was delivered to the work          random effects. The linear effect of the
Because grams of fiber per 1000 calories       sites randomized to the intervention con-       work site baseline mean for the variable
and servings of fruits and vegetables were     dition, a process-tracking system was           being analyzed was included as a covari-
skewed toward higher values, these vari-       developed to monitor achievement of the         ate. The effect of the intervention was
ables were transformed to a logarithmic        process objectives specified in the interven-   evaluated by the square root of the ratio
scale (ln(x) for fiber and ln(1 + x) for       tion protocol.'0 An a priori listing of the     of the mean square for treatment to the
fruits and vegetables) in order to make        number and type of interventions ex-            mean square for treatment by block
the distribution of the data approximately     pected at each work site yielded 15             interaction and was compared to a t
normal. The observed means and differ-         process objectives aimed at individual          distribution. The degrees of freedom for
ences as well as the covariate adjusted        change in the two risk factors plus             the significance levels presented are based
differences are presented here trans-          attendance at the kickoff; additional pro-      on the numbers of work-site pairs. There-
formed back into original units. Servings      cess objectives targeted change in the          fore, the analysis can be regarded as a
of fruits and vegetables were calculated       worksite environment.10 A computerized          weighted paired t test, made more effi-
on the basis of two questions about usual      relational database management system           cient since the work sites vary in size. For
intakes of fruit (excluding juice) and         documented the types of activities imple-       binary response variables (6-month smok-
vegetables (excluding potatoes and sal-        mented, the materials distributed, the          ing abstinence rate and smoking preva-
ads). The number obtained was added to         time and resources expended, and other          lence at final survey), mixed model logistic
the responses to items about salad, po-        pertinent factors. To assess the delivery of    regression was used,23'24 where the center
                                               intervention, the mean proportion of            and treatment arm were fixed effects, and
tato, and fruit juice servings (weighted for
serving size).'8                               process objectives achieved in each work        the block and arm-by-block interaction
                                               site was summed and was divided by the          were random effects. The effect of the
      Smoking outcomes. Analyses of two        number of work sites.                           intervention was evaluated by the ratio of
smoking outcomes were conducted with                  In general, process data were re-        the restricted maximum likelihood estima-
data from only the three study centers at                                                      tion of the regression coefficient for
                                               corded by research intervention staff, with
which smoking interventions were con-          the exception of MD Anderson. Because           treatment arm to its standard error and
ducted (Brown, Dana-Farber, and MD             of its unique use of participatory strate-      was compared with a normal distribu-
Anderson):                                     gies and its widely dispersed work sites,       tion.23 Secondary analyses were done by
      (1) The 6-month abstinence rate          MD Anderson relied on work-site employ-         adding age, gender, and education level
was measured by self-reported abstinence       ees to function as intervention coordina-       into the models as covariates.
for the 6 months prior to the survey.10 The    tors to implement and document interven-              Two alternative analyses were con-
denominator included all individuals who       tions, and as a result, some intervention       ducted to examine the robustness of the
had been employed by the work site for a       activities were underreported.                  results: (1) the generalized estimating
minimum of 6 months and who either                   Assessment of receipt of the interven-    equation,25 and (2) an analysis of the
were current smokers or had quit smoking       tion. With data from the individual em-         mean changes within each work site pair,
during the 2-year intervention period. A       ployee survey, two indices for each risk        by means of a bootstrap t test.26 Although
6-month abstinence rate has been used by       factor were created to calculate receipt of     data are not presented, the two analyses
many trials as a reasonable approximation      the intervention. The first index included      had results similar to those of the mixed
of continuous, long-term cessation.20'21       items that measured awareness of inter-         models, with the analyses at the work-site
      (2) Work site smoking prevalence         vention activities. The second index as-        level providing somewhat more conserva-
was also measured at baseline and in the       sessed activities that were directed toward     tive results owing to equal weighting for
final survey. Current smokers were de-         behavior change. For both indices, items        all work sites, which are of substantially
fined as individuals who had smoked at         were scored 1 or 0; the items were added        different sizes.
least 100 cigarettes in their lives and        and were divided by the total number of               Analyses were also conducted to
currently smoked at least 1 cigarette per      items. Weighting was considered but was         assess differences in the intervention

July 1996, Vol. 86, No. 7                                                                            American Journal of Public Health 941
Sorensen et al.

   TABLE 1-Nutrition Outcomes at Baseline and Follow-Up at Working Well Trial Work Sites, by Study Center

                                                          Brown            Dana-Farber            Florida        MD Anderson          All Centers
                                                         (n = 20             (n = 24              (n = 24           (n = 40             (n = 108
                                                       Work Sites)         Work Sites)          Work Sites)       Work Sites)         Work Sites)

                                                                      % energy from fat
    Intervention sites
      Baseline                                         35.42             35.83                 36.81             38.43              36.71
      Follow-up                                        33.30             33.83                 34.36             36.29              34.64
      Difference (follow-up minus baseline)            -2.12             -2.00                 -2.45             -2.14              -2.07
    Control sites
      Baseline                                         35.26             35.54                 36.66             39.00               36.70
      Follow-up                                        33.67             34.17                 34.71             36.90               35.00
      Difference (follow-up minus baseline)            -1.59             -1.37                 -1.95             -2.10              -1.70
    Difference (intervention minus control)
     Baseline                                           0.16              0.29                  0.15             -0.57               0.01
     Follow-up                                         -0.37             -0.34                 -0.35             -0.61              -0.36
     Difference (follow-up minus baseline)             -0.53             -0.63                 -0.50             -0.04              -0.37*
   Adjusted differencea (SE)                           -0.42 (0.27)      -0.43 (0.36)          -0.56 (0.47)      -0.09 (0.30)       -0.35* (0.16)

                                                                Dietary fiber, g/1000 kcals
    Intervention sites
      Baseline                                           7.92              8.02                  8.72              7.83               8.03
      Follow-up                                          8.76              8.59                  9.20              8.33               8.61
      Difference (follow-up minus baseline)              0.84              0.57                  0.48              0.50               0.58
    Control sites
      Baseline                                           7.89              8.06                  8.35              7.80               7.96
      Follow-up                                          8.44              8.45                  8.69              8.25               8.41
      Difference (follow-up minus baseline)              0.55              0.39                  0.34              0.45               0.45
    Difference (intervention minus control)
      Baseline                                           0.03            -0.04                   0.37              0.03               0.07
      Follow-up                                          0.32             0.14                   0.51 *            0.08               0.20*
      Difference (follow-up minus baseline)              0.29             0.18                   0.14*             0.05               0.13
      Adjusted percent increasea (SE)                    0.95 (2.1)       2.1 (1.2)              5.6* (2.2)        1.4 (1.5)          1.7 (0.87)

                                                        Servings of fruits and vegetables per day
    Intervention sites
      Baseline                                           2.69              2.71                  2.66              2.40               2.60
      Follow-up                                          2.82              2.99                  2.97              2.55               2.80
      Difference (follow-up minus baseline)              0.13              0.28                  0.31              0.15               0.20
    Control sites
      Baseline                                           2.66              2.74                 2.60               2.37                2.58
      Follow-up                                          2.66              2.83                 2.58               2.38                2.60
      Difference (follow-up minus baseline)              0.00              0.09                -0.02               0.01                0.02
    Difference (intervention minus control)
      Baseline                                           0.03             -0.03                  0.06              0.03                0.02
      Follow-up                                          0.16              0.16*                 0.39**            0.17*               0.20***
      Difference (follow-up minus baseline)              0.13              0.19*                 0.33**            0.14*               0.1 8***
    Adjusted percent increasea (SE)                      3.9 (3.7)         5.3* (1.7)           1 1.7** (3.5)      5.8* (2.3)          5.6*** (1.3)

    Note. SE = standard error.
    aBaseline work site mean value is added as a covariate.
    *P < .05; **P < .01; ***P < .001.

effect for subgroups with high vs low                   the statistical significance of the effect of     intervention and control work-site means
response rates. MD Anderson's data were                 the interaction of treatment arm by               within blocks. These pairwise differences
not used for this analysis since this study             response group. In this analysis, the             were regressed against experimental de-
center used a different method of survey                blocking effect was dropped from the              sign covariates employing bootstrap regres-
administration, which resulted in high                  model, since some pairs were broken               sion methods.26 Two sets of predictor
response rates, thus confounding the                    when the work sites were classified as            variables were employed: an intercept-
response rate with the center effect. Two               having high or low response rates.                only model and a model with center
response-rate subgroups were created                         Analyses of the receipt of interven-         effects added to the regression. The
( < 65% and > 65%). Analyses examined                   tion examined the difference between              intercept-only model was fit for each

942 American Journal of Public Health                                                                                           July 1996, Vol. 86, No. 7
                                                                                                                    Work-Site Cancer Prevention

   TABLE 2-Observed Proportion of 6-Month Smoking Abstinence and Smoking Prevalence at Final Employee Survey,
            by Study Center

                                                            Brown                Dana-Farber           MD Anderson              All Centers
                                                             (n= 20                (n = 24                (n = 40                 (n = 84
                                                         Work Sites), %         Work Sites), %         Work Sites), %          Work Sites), %

   6-month abstinence rate (% of quitters in total)
     Intervention sites                                 12.3                  17.3                    11.5                     13.8
     Control sites                                      11.2                  12.7                    12.9                     12.3
     Dffference (intervention minus control) (95% Cl)    1.04 (-2.5, 6.1)      4.61 * (0.25, 9.6)     -1.49 (-4.8, 2.1)         1.53 (-1.0, 3.7)
   Smoking prevalence (% of smokers in total)
     Intervention sites                                 24.8                  20.3                    19.5                 21.2
     Control sites                                      24.5                  21.4                    19.9                 21.8
     Difference (intervention minus control) (95% Cl)    0.37 (-7.2, 5.5)     -1.06 (-3.8, 2.7)       -0.42 (-2.5,1.7)     -0.66 (-3.0,1.2)

   Note. Cl = confidence interval.
   alntervention minus control.
   *P < .05.

individual study center and for all centers
combined. The model with center effects
added was used to examine whether the               TABLE 3-Work Sites' Achievement of Process Objectives, by Study Center
treatment effect differed among study
centers.                                                                                            % Process Objectives Achieved
    In all analyses, two-sided tests were                                                     Dana-             MD    All Centers
used and no multiple comparison adjust-                    Process Objectivea           Brown Farber Florida Anderson Combined
ments were made.
                                                    Kickoff participation (50% of          48        60        69         84             68
Response Rate Analyses                                                                     Nutritionb
     At baseline, the overall response rate         No. work sites                         11       12        12          20             55
                                                    Interactive kickoff activity (1)      100       92       100          95             96
to the individual survey was 69% (average           Posters (4)                           100       98       100          51             82
work-site response rate, 72%; study cen-            Video/single session                   97       83       100          68             84
ter mean range, 61% to 89%). The overall              presentation (3)
response rate at the follow-up survey was           Self-assessment activity (2)          100        100     100          68             88
                                                    Self-help program (2)                 100         96      96          45             78
71% (average work-site response rate,               Multisession direct education (2)     100         92     100          20             69
75%; study center mean range 68% to                 Campaign (1)                          100         92       92         50             78
86%). The interaction of the response-                   Total                            100         93       98         57             82
rate subgroup (cutpoint, 65%) and the
intervention group indicated no relation-                                                  Smokingb
ship between the intervention effects and           No. work sites                         11     12          NA          20             43
the work site's response rate to the                Interactive kickoff activity (1)      100     92          NA          45             72
individual survey (smallest P = 0.24).              Posters (4)                            98     92          NA          66             81
                                                    Video/single session                   91     56          NA          62             67
Nutrition                                             presentation (3)
                                                    Self-assessment activity (2)           91         96      NA          75             85
     For percentage of energy obtained              Self-help program (2)                 100        100      NA          60             81
from fat consumption, there was a net               Multisession direct education (2)     100         58      NA          35             58
                                                    Campaign (1)                          100         83      NA          50             72
decrease of 0.37 percentage points                                                         97         82      NA          56             74
(P = .033) (see Table 1). Results for each
of the four study centers showed a trend            Note. NA = not applicable.
in the desired direction, although only the         aExcludes process objectives directed toward environmental change; numbers in parentheses
combined results were statistically signifi-          indicate the number of times an activity was to be done.
                                                    bConducted in each intervention work site.
     Also as shown in Table 1, the net
increase in fiber consumption was only
0.13 g per 1000 kcal (P = .056), since           increase of 0.14, P = 0.024) were statisti-         intervention sites and      was   negligible in
control-site employees also increased fi-        cally significant. The intake of fruits and         most control sites.
ber intake an average of 0.45 g. Results         vegetables increased a net average of 0.18          Smoking
for three of the four study centers showed       servings per day for all study centers
a trend in the desired direction, although       (P .0001). Increased fruit and vegetable
                                                    =                                                     For the trial overall, there was a
only the results for Florida work sites (net     consumption was consistently higher in              nonsignificant difference of 1.53% in the

July 1996, Vol. 86, No. 7                                                                                  American Journal of Public Health 943
Sorensen et al.

                                                                                                         behavior after a sustained 2-year interven-
   TABLE 4-Bootstrap Regression Estimates for Awareness and Action Indexes,                              tion. A common intervention protocol
            by Study Center                                                                              was applied to the four study centers,
                                                                                                         covering 111 work sites that were ran-
                                      Intervention-Control                                               domly assigned to intervention or control
    Awareness/ Action Index                Difference                SE       P         95% Cl           conditions. The study had sufficient power
                                                                                                         for study center-specific evaluations as
   Smoking awareness                                                                                     well as for data from all sites combined.
     Brown                                     0.15                 0.09     0.15     -0.05, 0.36
     Dana-Farber                               0.09                 0.06     0.15     -0.02, 0.28        Results presented here focused on the
     MD Anderson                               0.16                 0.04     0.00       0.08, 0.27       combined data reflecting individual behav-
        All centers combined                   0.14                 0.03     0.00       0.08, 0.22       ior changes. The work site was the unit of
   Nutrition awareness                                                                                   randomization, intervention, and analysis.
      Brown                                    0.22                 0.07     0.02       0.05, 0.40       Analyses were also conducted to elimi-
     Dana-Farber                               0.22                 0.05     0.00       0.10, 0.33       nate the possibility of response-rate bias.
     Florida                                   0.14                 0.03     0.01       0.09, 0.24            For the trial as a whole, significant
     MD Anderson                               0.15                 0.04     0.00       0.07, 0.24
        All centers combined                   0.17                 0.02     0.00       0.13, 0.22       results were observed for two of three
   Smoking action                                                                                        individual nutrition outcomes. Although
     Brown                                     0.18                 0.04     0.01       0.11,   0.30     the percentage of energy obtained from
     Dana-Farber                               0.12                 0.01     0.00       0.10,   0.17     fat consumption decreased by 2.07 per-
     MD Anderson                               0.18                 0.03     0.00       0.13,   0.24     centage points between baseline and
        All centers combined                   0.13                 0.02     0.00       0.10,   0.17     follow-up, the percentage of energy from
   Nutrition action                                                                                      fat decreased 1.70 percentage points
     Brown                                     0.31                 0.03     0.00       0.25, 0.40       among employees in the control sites. The
     Dana-Farber                               0.24                 0.03     0.00       0.18, 0.29
     Florida                                   0.32                 0.02     0.00       0.26, 0.37       level of change observed in control sites
     MD Anderson                               0.20                 0.04     0.00       0.13, 0.29       suggests a modest secular trend in the
        All centers combined                   0.26                 0.02     0.01       0.22, 0.29       reduction of fat consumption. The largest
                                                                                                         net effect for nutrition was change in the
   Note. SE = standard error; Cl = confidence interval.                                                  consumption of fruits and vegetables.
                                                                                                         Intake of fruits and vegetables increased
                                                                                                         an average of 0.18 servings for all study
                                                                                                         centers; one study center obtained a
6-month quit rates between intervention                   centers. For the trial overall, process        difference of approximately a third of a
and control work sites (see Table 2).                     objective attainment in this risk factor was   serving.
     We also examined changes in smok-                    high, with an overall 82% of process                 The increased intake of fruits and
ing prevalence, although sufficient power                 objectives attained. Process objectives        vegetables may be interpreted, for ex-
for this outcome was not part of the                      attained for smoking-control activities        ample, as a change in one fifth of a serving
design of the Working Well Trial. As                      were not as high as for nutrition, with an     for every individual or as one person in
shown in Table 2, smoking prevalence                      overall trial attainment of 74%.               five having increased consumption by a
dropped considerably in both the interven-                                                               full serving. Results reported here repre-
tion (from 24.5% to 21.2%) and control                    Receipt of Intervention                        sent changes occurring in the entire
(from 25.8% to 21.8%) conditions in the 2                      Cronbach's alpha was computed for         work-site population, among employees
years of the trial.                                       each receipt index, and values were found      in intervention sites who actively partici-
                                                          to be uniformly high (range = .78 to .85).     pated in the intervention as well as those
Delivery of the Intervention                              Table 4 shows the treatment effects on the     who were unaware of the program. Addi-
     The duration of the intervention                     receipt of the intervention activities by      tional analyses are needed to assess
varied, with the median (and range)                       study center and for the trial overall. The    whether small changes were made by a
number of weeks between the kickoff                       center-by-treatment-condition interac-         majority of respondents or whether there
event and the final survey at the four study              tion was tested for each index, and no         were larger changes concentrated among
centers as follows: at Brown, 120 (117 to                 significant interactions were observed.        fewer individuals. Although such changes
125); at Dana-Farber, 97 (82 to 120); at                  For each of the receipt indices, an            are small in clinical terms, they may be
Florida, 121 (102 to 123); and at MD                      intervention-minus-control difference was      indicative of a potentially important pub-
Anderson, 97 (80 to 104).                                 significant (P < .001). The data provide       lic health impact if they are maintained
     Table 3 shows the percentage of the                  evidence that intervention materials and       and are cumulative, when we consider the
process objectives achieved by study cen-                 activities reached employees in the work       large numbers of workers represented by
ter and for all study centers combined.                   sites; furthermore, these materials and        this trial.
The process objective that required that                  activities were utilized to a greater extent         The intervention failed to produce
50% of employees attend the overall                       than any programs or materials available       statistically significant differences be-
kickoff event was met by all study centers                in control work sites.                         tween intervention and control sites for
except Brown, where average work-site                                                                    measures  of smoking. Only at one study
kickoff participation was 48%. Overall                                                                   center, Dana-Farber, was the difference
                                                          Discussion                                     in 6-month quit rates statistically signifi-
participation in the kickoff averaged 68%.
     For nutrition, there was high delivery                   The Working Well Trial measured            cant. This significant finding in one site
of the intervention in three of the four                  changes in eating patterns and smoking         suggests that effective work-site smoking

944 American Journal of Public Health                                                                                         July 1996, Vol. 86, No. 7
                                                                                                                Work-Site Cancer Prevention

cessation interventions may be possible;         were significantly higher in the interven-     impact of variations in levels of delivered
there still remains the important chal-          tion sites than in control sites. Respon-      and received interventions, policy changes,
lenge of determining how best to inter-          dents were more likely to report aware-        and participatory strategies on the ob-
vene in work sites to promote smoking            ness of nutrition- than smoking-related        served outcomes will be explored in future
cessation. Additional analyses will exam-        intervention activities, perhaps because       papers. The interaction of multiple risk
ine the role of work site characteristics in     nutrition is important to more people          factor interventions, as implemented and
the observed changes.                            than is smoking. Similarly, a greater          sequenced at various work sites, may have
      The changes in smoking behavior            percentage of nutrition- than smoking-         contributed to center differences in ob-
observed in these intervention work sites        related process objectives were achieved;      served outcomes.
compare favorably with abstinence rates          this probably contributed to the observed            Finally, the 2-year duration of the
reported in previous minimal intervention        differences in significant outcomes for        Working Well Trial intervention may not
trials'9 and with reductions in smoking          nutrition. The analyses of the receipt of      have been long enough to observe the
prevalence reported by similar work site-        intervention indices also underline the        intended effects, owing to several features
based interventions.27 However, the con-         high level of intervention activity in         of the intervention design. First, the
trol group's 6-month smoking abstinence          control work sites, reflecting the secular     Working Well Trial intervention used the
rate (11.2%) is somewhat higher than             trend toward increasing health promotion       stage-of-change model to develop an
expected, based on several comparable            efforts at the work site.                      intervention that emphasized awareness,
prior reports. For example, a recent                   The intervention protocol also aimed     active change, and maintenance activities
examination of 10 prospective studies of         to promote the adoption of work-site           at the work site, with the understanding
self-quitters found a median 6-month             smoking bans and increase the availability     that change occurs in small increments in
abstinence rate of 6.0%.21 Similarly, the        of healthy foods at the work place since       a cyclical pattern over time.41 A longer
1987 National Health Interview Survey            behavior change and its maintenance            intervention period may be needed to
found that only 6.0% of ever-smokers who         requires a supportive social environ-          observe the movement of individuals
attempted to quit in the past 12 months          ment.31-33 It was beyond the scope of this     through the varying stages of readiness for
were continuously abstinent for more             paper to present changes in the work site      change. Second, following a participatory
than 3 months.28 At the Working Well             environment resulting from this interven-      strategies model, employee advisory
baseline, the 4- to 12-month continuous          tion.                                          boards were formed to provide worker
abstinence rate was 6.0%."1 This increase              Several limitations must be noted in     input into intervention planning and
in quit rates within the control group may       the interpretation of these results. For       implementation. Organization and main-
reflect the high level of smoking-related        both nutrition and smoking outcomes,           tenance of these boards required substan-
intervention activities at control sites, as     self-reports were used to assess change in     tial investments of time and in some cases
indicated by the data on the receipt of the      the outcome variables. For nutrition, the      may have delayed the start-up of interven-
intervention. Some control sites also re-        food-frequency questionnaire was previ-        tion delivery.
ceived minimal interventions such as the         ously validated.-3439 However, the need              In conclusion, the Working Well
distribution of posters and brochures. In        for biochemical validation of smoking          Trial work-site intervention resulted in
particular, smoking policy awareness and         cessation in field studies such as this has    small but significant decreases in fat
implementation at all work sites was high;       been increasingly challenged.28,40             consumption and increases in fruit and
contributing to this trend may have been               Work sites were not randomly se-         vegetable intake. The potential public
the release, midway through the trial, of        lected for inclusion in this study; although   health significance of such small changes
the Environmental Protection Agency              a wide range of company types and              must be debated within the context of the
report on environmental tobacco smoke            geographic regions were included, these        work site-wide nature of this intervention
as a carcinogen.29                               results should be generalized only to          and its evaluation. Although significant
      More powerful intervention strate-         similar work sites. Baseline results sug-      smoking cessation differences were not
gies may be needed to increase smoking           gested that both intervention and control      observed trial-wide, the success of one
cessation rates beyond the current secular       work sites were more likely to have had        study center in achieving a significant
trend noted in the Working Well Trial            health promotion activities than worksites     difference in cessation suggests the oppor-
control work sites. This trial used a            nationwide," a selection bias that may         tunity for future initiatives if the compo-
state-of-the-art intervention model based        have contributed to the high level of          nents and attributes of successful cessa-
on participatory public health strategies.30     behavior change in the control work sites.     tion interventions can be identified. For
Some possible ways of increasing the             By necessity, only work sites where there      both the nutrition and smoking outcomes,
potency of the intervention are to provide       is interest in health promotion are likely     sizable secular trends observed during the
programming of increased intensity and           to be enrolled in studies such as these.       study period may have accounted for
duration, to integrate the health promo-               Centers and work sites differed in a     some of the reduced magnitude of the
tion intervention with an intervention           number of dimensions, which certainly          observed differences between interven-
targeting occupational health and safety         influenced uniform application of the          tion and control groups. Process-tracking
or other health-related concerns of work-        intervention. Although a common inter-         data supported the overall integrity of the
ers, to incorporate the use of pharmaco-         vention protocol was used, there were          delivery of the intervention, and worker
logical aids, and to target specific types of    variations in the combination of risk          data showed significantly greater aware-
work sites or workers, such as disadvan-         factors addressed and in the intensity of      ness of and participation in nutrition and
taged or young smokers.                          the contacts with the work sites (e.g., work   smoking-control activities in intervention
      Consistently, the intervention receipt     sites at MD Anderson were scattered            sites. If more substantial changes are to be
indices, which compared employee re-             across 11 states and therefore had less        expected throughout the entire work-site
ports of the level of intervention activities,   intensive contact with project staff). The     population, future work-site interventions

July 1996, Vol. 86, No. 7                                                                             American Journal of Public Health 945
Sorensen et al.

may need to reexamine the intensity and               Allan Williams. Programmers: Stephanie                   conceptual and practical considerations.
duration of interventions, the sequencing             Stafford, Peter Dueber, Lynette Brown (1990-             In: Richmond R, ed. Interventions for
and timing of environmental interven-                 1991). Cost analysts: Shelly Hager, Addy                 Smokers: An International Perspective.
                                                      Tseng, Carole Shaw (1990-1993). Support                  Baltimore, Md: Williams & Wilkins, 1994:
tions, and the potential synergism of                 staff: Catherine Cohen, Ellen Powell (1991-              137-170.
multiple risk factor interventions. El                1992), Estella Bennett (1990-1992), Jenny           6.   Erfurt JC, Foote A, Heirick MA. Worksite
                                                      Devaney (1990-1991).                                     wellness programs: incremental compari-
                                                      Working Groups and Subcommittees                         son of screening and referral alone, health
Acknowledgments                                              Steering Committee: Ed Lichtenstein               education, follow-up counseling, and plant
This work was supported by a Cooperative              (Chair), David B. Abrams, Ellen R. Gritz,                organization.Am JHealthPromotion. 1991;
Agreement from the National Cancer Institute,         James Grizzle, Jerianne Heimendinger, Glo-               5:438-448.
Grants UOI CA51687, UO1 CA61771, UO1                  rian Sorensen, Jill Varnes, W. Bryant Boutwell      7.   Jeffery RW, Forster JL, French SA, et al.
CA51686, UO1 CA516888, and P01 CA50087.               (1991-1993), Michael Ericksen (1989-1991),               The Healthy Worker Project: A work-site
      The investigators and committee mem-            Ellen Gritz (1993-1994).                                 intervention for weight control and smok-
bers for the Working Well Trial are as follows:             Data Managers/ Tracking Coordinators: Al-          ing cessation. Am J Public Health. 1993;83:
      National Cancer Institute (NCI), Division       lan Williams (Chair), Peter Dueber, James                395-401.
of Cancer Prevention and Control. Program             Eldridge, Kathy Galloway, Susan Gucken-             8.   Sorensen G, Morris D, Hunt MK, et al.
director: Jerianne Heimendinger. Statisticians:       berger, Jean Hsieh, Cynthia Lostoski, Steve              The effects of a worksite nutrition interven-
Charles Brown, Don Corle. Fellows: Nancy              Potter, Stephanie Stafford, David Vampola,               tion on employees' dietary habits: the
Cotugna (1990), Susan Sullivan (1990-1991).           Kate Lapane (1989-1992).                                 Treatwell program. Am J Public Health.
Study Centers                                               Evaluation Working Group: James Grizzle            1992;82:877-880.
      Brown University School of MedicinelThe         (Chair), Don Corle, James Eldridge, David           9.   Glasgow RE, Terborg JR, Hollis JF,
Miriam Hospital. Principal investigator: David        Miller, Anne Stoddard, Wayne Velicer.                    Severson HH, Boles SM. Take Heart:
B. Abrams. Co-principal investigator: Lois                  Nutrition Working Group: Karen Glanz               results from the initial phase of a work-site
Biener. Co-investigators: Karen M. Emmons,            (Chair), James Hebert, Jerianne Heimend-                 wellness program. Am J Public Health,
Laura Linnan. Statisticians: Joe Fava, Wayne          inger, Mary Kay Hunt, Alan Kristal, Laura                1995;85:209-216.
Velicer. Project director: Laura Linnan. Inter-       Linnan, Ruth Patterson, Claudia Probart.           10.   Abrams DB, Boutwell WB, Grizzle J,
vention specialists: Edward Galuska, Mary             Additional Nutrition Intervention Subcommittee           Heimendinger J, Sorensen G, Varnes J.
Lynne Hixson, Sheila Jacobs, Suzanne Mori-            Participants: Mary Lynne Hixson, Judith Phill-           Cancer control at the workplace: the
arty. Data specialist: David Vampola, Kate            ips, Patricia Pillow.                                    Working Well Trial. Prev Med. 1994;23:
Lapane (1989-1992). Research associate: Ja-                  Organizational Variables Working Group:           1-13.
nine Costa. Administrative assistant: Mark            Lois Biener (Chair), Susan Kinne (Cochair),        11.   Heimendinger J, Feng Z, Emmons K, et al:
Morgenstern.                                          Karen Basen-Engquist, Jerianne Heimend-                  The Working Well Trial: Baseline dietary
      Dana-Farber Cancer Institute! University of     inger, Glorian Sorensen, Jill Varnes.                    and smoking behaviors of employees and
Massachusetts Medical SchooL Principal investi-              Process Evaluation Working Group: Glo-            related worksite characteristics. Prev Med.
gator: Glorian Sorensen. Co-principal investiga-      rian Sorensen (Chair), Karen Basen-Engquist,             1995;24:180-193.
tors: Jay Himmelstein, Judith Ockene. Co-             Shelly Hager, Jean Hsieh, Mary Kay Hunt,           12.   Abrams DB, Elder JH, Carleton RA, et al.
investigators: Katharine Hammond, James               Laura Linnan, Cynthia Lostoski, David Miller,            Social learning principles for organiza-
Hebert, Ruth Palumbo, Anne Stoddard. Project          Stephanie Stafford, Addy Tseng, Nicole Urban             tional health promotion: an integrated
director: Mary Kay Hunt. Evaluation coordina-         (1990-1992).                                             approach. In: Cataldo MF, Coates TJ, eds.
tor: Jean Hsieh. Intervention coordinators:                 Participatory Strategies Working Group:            Health and Industry: A Behavioral Medicine
Lynda Graham-Meho, Elizabeth Harden, Jane             Claudia Probart (Chair), Karen Basen-En-                 Perspective. New York, NY: Wiley; 1986:
Ellen Thompson. Nutrition coordinator: Judith         gquist, Karen Emmons, Jerianne Heimend-                  28-51.
Phillips. Industrial hygienist: Richard Young-        inger, Mary Kay Hunt, Laura Linnan, Ingrid         13.   Abrams DB. Conceptual models to inte-
strom. Process tracking coordinator: Steve            Nielsen, Beti Thompson.                                  grate individual and public health interven-
Potter. Administrative assistant: Elizabeth Farr.           Publications and Presentations Subcommit-          tions: the example of the workplace. In:
      University of Florida at Gainesville. Princi-   tee: Jill Varnes (Co-Chair), Karen Emmons                Henderson M, chair. Proceedings of the
pal investigator: Jill Varnes. Co-principal inves-    (Cochair 1991-1992, 1994), Ziding Feng, Ellen            International Conference on Promoting Di-
tigator: Claudia Probart. Co-investigator, medi-      R. Gritz, Jerianne Heimendinger, Anne Stod-              etary Change in Communities. Seattle, Wash:
cal consultant: David Schapira. Statistician:         dard, David B. Abrams (Chair 1989-1991), W.              The Fred Hutchinson Cancer Research
David Miller. Intervention coordinators: Jean-        Bryant Boutwell (Cochair, 1992-1993).                    Center, 1991:173-194.
ine Lahey, Steve Livesay, Valerie Studnick                  Smoking Working Group: Karen Emmons          14.   Rothman J. Three models of community
(1990-1992). Interventionist/ tracking coordina-      (Chair), Carlo DiClemente (Chair 1989-1991),             organizational practice. In: Cox FM, ed.
tor: Susan Guckenberger. Office manager, data         Jerianne Heimendinger, Judith Ockene, Beti               Strategies of Community Organization. Itasca,
manager: Kathy Galloway.                              Thompson, David B. Abrams (1989-1992).                   Ill: FE Peacock Publishers, 1970.
      University of Texas M.D. Anderson Cancer                                                           15.   Bracht JF, ed. Health Promotion at the
Center. Principal investigator: Ellen R. Gritz,       References                                               Community Level. Newbury Park, Calif:
W. Bryant Boutwell (1991-1993), Michael                1. American Cancer Society. Cancer Facts                Sage Publications, 1990.
Ericksen (1989-1991). Co-principal investiga-             and Figures: 1993. Atlanta, Ga: American       16.   Kristal AR, Shattuck AL, Williams AE.
tor: Carlo DiClemente. Co-investigators: Rob-             Cancer Society; 1993.                                Food frequency questionnaires for diet
ert Chamberlain, Guy Parcel, Karen Basen-              2. Doll R, Peto R. The causes of cancer:                intervention research. In: Proceedings of the
Engquist, John Foryet, Larry Whitehead, Alan              Quantitative estimates of avoidable risks of         17th National Nutrient Data Bank Confer-
Herd, Jane Mayfield. Project coordinator:                 cancer in the United States today. JNCI              ence, June 7-10, 1992. Washington, DC:
Scott R. Cummings. Intervention specialists:              1981;66:1191-1308.                                   International Life Sciences Institute; 1994:
Scott R. Cummings, Ingrid Nielsen, James               3. Greenwald P, Sondik E, eds. Cancer                   110-125.
Eldridge, Bill Mann. Consultants: Karen Glanz,            Control Objectives for the Nation, 1985-       17. Glanz K, Patterson RE, Kristal AR, Di-
Robert Butera.                                            2000. Washington, DC: National Cancer              Clemente CC, Heimendinger J, Linnan L.
Coordinating Center: Fred Hutchinson Cancer               Institute; 1986.                                   Stages of change in adopting healthy diets:
Research Center. Principal investigator: James         4. Klesges RC, Cigrang JA. Worksite smok-             fat, fiber, and correlates of nutrient intake.
 Grizzle. Co-investigators: Ziding Feng, Susan            ing cessation programs: clinical and meth-         Health Educ Q. 1994;21(4):73-93.
 Kinne, Alan Kristal, Beti Thompson, Nicole               odological issues. In: Hersen M., Eisler       18. Block G. Health Habits and History Question-
 Urban (199(}1992). Fellow: Ruth Patterson.               R.M., Miller R.M., eds. Progress in Behav-         naire: Diet History and Other Risk Factors.
 Coordinating center manager: Sonya Olsen,                ioral Modification. Vol 23. Newbury Park,          Bethesda, Md: National Cancer Institute;
 Gwen Glaefke (1989-1992). Statistical re-                Calif: Sage Publications; 1988:37-61.              1988.
 search associates: Cynthia Lostoski, Steve            5. Abrams D, Emmons K, Linnan L, Biener           19. Schakel SF, Sievert TA, Buzzard IM.
 Thomson, Dale McLerren. Database manager:                L. Smoking cessation at the workplace:             Sources of data for developing and main-

946 American Journal of Public Health                                                                                              July 1996, Vol. 86, No. 7
                                                                                                                              Work-Site Cancer Prevention

      taining a nutrient database. J Am Diet               Centers for Disease Control; 1990. DHHS          35. Block G, Woods M, Potosky A, Clifford C.
      Assoc. 1988;88:1260-1271.                            publication (CDC) 90-8416.                           Validation of a self-administered diet his-
20.   COMMIT Research Group. Community               29.   Respiratory Health Effects of Passive Smok-          tory questionnaire using multiple diet
      Intervention Trial for Smoking Cessation             ing: Lung Cancer and Other Disorders: The            records. J Clin Epidemiol. 1990;43:1327-
      (COMMIT): summary of design and inter-               Report of the Environmental Protection               1335.
      vention. JNCI. 1991;83:1620-1628.                    Agency. Washington, DC: US Environmen-           36. Sobell J, Block G, Koslowe P, Tobin J,
21.   Cohen S, Lichtenstein E, Prochaska JO, et            tal Protection Agency; 1993.                         Andres R. Validation of a retrospective
      al. Debunking myths about self-quitting.       30.   Thompson B, Kinne S. Social change                   questionnaire assessing diet 10-15 years
      Am Psychol. 1989;44:1135-1365.                       theory: applications to community health.            ago.AmJEpidemioL 1989;130:173-187.
22.   Searle R, Casella G, McCulloch CE.                   In: Bracht N, ed. Health Promotion at the        37. Block G, Thompson FE, Hartman AM,
      Variance Components. New York, NY.                   Community Level. Newbury Park, CA: Sage              Larkin FA, Guire KM. Comparison of two
      John Wiley, 1992.                                    Publications; 1990;45-65.                            dietary questionnaires validated against
23.   Schall R. Estimation in generalized linear     31.   Thompson B, Wallack L, Lichenstein E,                multiple dietary records collected during a
      models with random effects. Biometrika.              Pechacek T, for the COMMIT Research                  1-year period. JAAL4. 1992;92:686-693.
       1991;78:719-727.                                    Group. Principles of community organiza-         38. Coates RJ, Eley JW, Block G, et al. An
24.   Wolfinger R. Laplace's approximation for             tion and partnership for smoking cessation           evaluation of a food frequency question-
      nonlinear mixed models. Biometrika. 1993;            in the Community Intervention Trail for              naire for assessing dietary intake of specific
      80:791-795.                                          Smoking Cessation (COMMIT). Intl Q                   carotenoids and Vitamin E among low-
25.   Liang KY, Zeger SL. Longitudinal data                Community Health Educ. 1991;11:187-203.              income Black women. Am J Epidemiol.
      analysis using generalized linear models.      32.   Green L, McAlister A. Macro-intervention             1991;134:658-671.
      Biometrika. 1986;73:13-22.                           to support health behavior change: some          39. Mares-Perlman JA, Klein BEK, Klein R,
26.   Efron B, Tibshirani RJ. An Introduction to           theoretical perspectives and practical reflec-       et al. A diet history questionnaire ranks
      the Bootstrap. New York, NY. Chapman &               tions. Health Educ Q. 1994;11:322-339.               nutrient intakes in middle-aged and older
      Hall, 1993.                                    33.   Wallack L, Wallerstein N. Health educa-              men and women similarly to multiple food
27.   DiClemente CC, Prochaska JO, Fairhurst               tion and prevention: designing community             records.JNutrEduc. 1993;123:489-501.
      S, Velicer WF, Velasquez M, Rossi J. The             initiatives. Intemational Q Community            40. Velicer WF, Prochaska JO, Rossi JS, Snow
      process of smoking cessation: an analysis of         Health Educ. 1986-87;7:319-342.                      M. Assessing outcome in smoking cessa-
      precontemplation, contemplation and            34.   Block G, Hartman AM. Dietary assess-                 tion studies. Psychol Bull. 1992;1 11:23-41.
      preparation.JConsultClinPsychol. 1991;59:            ment methods. In: Moon TE, Micozzi MS,           41. Prochaska JO, DiClemente CC, Norcross
      295-304.                                             eds. Nutrition and Cancer Prevention, Inves-         JC. In search of how people change:
28.    The Health Benefits ofSmoking Cessation:A           tigating the Role of Micronutrients. New             applications to addictive behaviors. Am
      Report of the Surgeon General. Atlanta, Ga:          York, NY: Marcel Dekker, 1989:159.                   Psychol. 1992;47:1102-1114.

July 1996, Vol. 86, No. 7                                                                                          American Journal of Public Health 947

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