Document Sample
Validity Powered By Docstoc
					              Social Support vs. Loneliness

• Condition                   Single         Married
•   Suicide                    25.8          12.2
•   Cirrhosis of liver          8.0           2.1
•   Motor vehicle accidents    58.8          35.6
•   T.B.                        6.9           1.4
•   Mean days hospitalized     19.2           9.8

                Loneliness and Health

Dr. James Lynch has argued in The broken heart: The medical
consequences of loneliness that social isolation leas to loneliness
which in turn is the cause of emotional deterioration followed by
actual physical deterioration. He cites higher coronary death rates
for Irish-Americans residing in Boston compared to those in Ireland
(where a more close-knit society is supposed to exist) and a higher
death rate in Nevada compared to neighbouring (and presumably
more family oriented Mormon Utah. What other explanation for
these results might be offered?
        Speeding and Highway Fatalities

After the energy crisis in the U.S., the highway speed limit was
lowered to 55 m.p.h. in an effort to conserve gasoline. In 1973
there were 55,000 highway fatalities. In 1974, there was a 20%
decrease in such fatalities, with a further 2% in 1975. In 1976,
highway fatalities increased, and this increase was attributed to a
rise in highway speeds. What other factors might have caused
fatalities to have increased during this time period?
                         Deadly Corvettes

Recent statistics indicated that the Corvette sports car is the most
dangerous vehicle on Canadian highways as measured by driver
deaths. This automobile has a fiberglass body and very large, powerful
engine which is placed in the front of the vehicle. There is no trunk and
the weight distribution is disproportionately in the forward position of the
vehicle. May we conclude that the design and construction of the
vehicle is responsible for causing driver deaths?
                       Cola Wars

  The Pepsi-Cola corporation decided to combat the 3:1 sales
lead of Coca-Cola in Dallas by commissioning a taste
preference study of Texans. Coke drinkers in Dallas were the
participants and were asked to indicate their preference for
either a sample drink of Coke or Pepsi. Since the testers did not
want to label the drinks by brand name, they placed the Coca-
Cola in glasses labeled “Q” and the Pepsi-Cola in glasses
labeled “M”. The results indicated a 2:1 preference of Coke
drinkers for Pepsi. Aside from obvious taste differences, what
other factors might have influenced beverage choice?

Consumer’s Reports Bread Nutrition Evaluation

The Consumer’s Union decided to test the nutritional value of 33
commercially produced American breads. Rather than evaluate the
posted nutritional label required on U.S. food products, they arranged
for a consultant to run an animal study. After a one-week period to
acclimate the rats to the lab, 36 groups consisting of six rats were
established. Three groups constituted the comparison group: one
group received lab rat food as a control, one was fed eggs and the
other, milk. All groups were provided unlimited quantities of their feed
along with water. The rats’ growth rate was studied, along with the
condition of the rat’s teeth and coat. Nervousness was measured as
were any abnormalities. The results indicated that one group of rats
feed a specific brand of bread (Thomas’ Rite Diet Bread) achieved
superior health compared to the other groups.
Assume that random assignment of all rats to treatment groups.
Can you suggest a rival hypothesis?
                     Boating Safety
There has been a recent shift in Canada to licence boaters. This
concern has developed over the high rate of accidents and
fatalities among boaters. Power boaters are disproportionately
involved in accidents compared to those in sailboats. May we
conclude that power boaters are inherently more dangerous
because of their large engines and speed? Why are the less
maneuverable sailboats not involved in as many accidents?

             The Case of the Dentist’s Drill

A survey of dental students at the University of Tennessee
found that they suffered a significant loss of hearing within three
years of using high speed drills. These instruments reduce a
patient’s discomfort, but seem to cause a hearing loss. The
researchers in Tennessee recommend that dentists wear
hearing protection on the job. What other factors might cause
these students to suffer hearing loss?
           Diffusion of Responsibility in Tipping

• In their work on diffusion of responsibility, Latané and Darley
  examined tipping behaviour of restaurant patrons. They found
  that solitary dinners were more generous tippers than groups of
  dinners and concluded that tipping is another example of
  individuals using the group to avoid performing normative
  obligations. What alternatives would you suggest?
 Diffusion of Responsibility in Charitable Donations

   Wiesenthal, Austrom, and Silverman (1983) established a
   charity drive for earthquake victims and examined the diffusion
   of responsibility in charitable donations. A student fundraiser
   approached other students seated either in groups, or by
   themselves, in various campus pubs. Solitary individuals were
   the most generous, while groups (especially larger groups) were
   noticeably stingier. While the data support the notion of
   diffusion of responsibility, what other explanations could be
   posed for these results?

Wiesenthal, D. L., Austrom, D., and Silverman, I. (1983). Diffusion of
   responsibility in charitable donations. Basic and Applied Research in
   Social Psychology, 4, 17-27.
     Bumper Stickers and Police Harassment

To investigate reports that the California State Police were
harassing black motorists in the late 1960s, a social
psychologist selected three groups of five students (white,
blacks, Chicanos) all of whom had excellent driving records.
They were to drive cars that had satisfactorily completed a
safety inspection. The cars either had a Black Panther Party
bumper sticker or a Support the Police sticker. The Panthers
had been in a number of violent confrontations with the police,
especially in California. Within 17 days, the drivers with the
Black Panther stickers had received 33 citations.

The authors claimed that the data supported the notion of police
harassment. Are other explanations possible?
                       Types of Validity
Internal: are the differences in the dependent variable (measure)
   due to the operation of the operation of the independent variable
   and not due to an extraneous (confounding) variable.

External (or ecological validity): the extent that the results
  generalize to the real world

Statistical: accuracy of the conclusion from a statistical test

Construct: the degree to which the theory(ies) behind the research
  provides the best explanation for the obtained results. How well
  do the results support the theories, models, constructs behind
  the research or/and do they provide the best available
  theoretical explanation for the results.
                       Types of Validity

Discriminant validity: when a measure does not correlate highly
   with a measure of a different construct. Example: a violence
   measure might have a degree of discriminant validity if it does
   not correlate with the measures of assertiveness, social
   desirability, and independence.
Convergent validity: the extent to which your measure correlates
   with other indicators of the construct.
               Threats to Statistical Validity

• Dependent variable (measure(s)) is (are) unreliable.

• Statistical assumptions underlying statistical tests have been
  violated (example: in t-tests and ANOVAs are the means and
  variances correlated? Are the distributions approaching
  normality or are they skewed?).
                       Internal Validity

Definition: The results of an experiment being attributable to the
  operation of the independent variable. It asks whether the
  obtained differences between the experimental condition or
  groups are really the result of the experimental manipulations.
                 Threats to Internal Validity

•   Reactivity
•   Reliability of measuring instruments/stimulus delivery
•   Inconsistent treatment administration
•   Selective subject loss
•   Experimenter bias
•   Nonrandom assignment
•   Contamination of the subject pool
•   Experimenter effects: active/passive
•   Subject role-related behaviours
•   Effects of previous testing (carryover effects)
•   Omission of a key (control) group
                    External Validity

Definition: To what extent can the present results
  generalize to other samples, situations, tasks.

Experiments lacking random assignment of subjects to
  treatment conditions and the absence of an
  independent variable manipulated by the
  experimenter. Example: automobile deindividuation

Shared By: