VIEWS: 3 PAGES: 38 POSTED ON: 9/22/2011
Survey Research AD700 College of Advancing Studies 13 October, 2004 Brendan Rapple This presentation owes much to the American Statistical Association brochure series on survey research: http://www.amstat.org/sections/srms/whatsurvey.html Little Cards on Restaurant Tables: Was the service good? Telephone: Is president doing a good job? The most popular programs on public radio? Census: How many bathrooms do you have? Magazines: How is your romantic life? Market Researchers: Brand X or Brand Y? How many drinks last week? Surveys Provide Important Knowledge Economists, psychologists, health professionals, political scientists, and sociologists conduct surveys to study such topics as: Income and expenditure patterns among households; Roots of ethnic or racial prejudice; Implications of health problems on people’s lives; Voting behavior; Effects on family life of women working outside the home, etc. Specific Purpose Essential Objectives of a survey should be as Specific Clear-cut Unambiguous as possible "Men's Health Practices" is a very nebulous topic. Better: How often do African-American males aged 40-49 visit the dentist? Steps in Conducting A Survey Define precise purpose Specify population Specify appropriate sample How to administer survey? Draft of survey instrument Pretest it Revise it Administer survey to sample Analyze, write it up, and communicate the results Use results meaningfully Decide on Mode of Data Collection Mail Telephone In Person Interview Computer Pre-Testing Critical for identifying questionnaire problems. Main problems revolve about: Question content, e.g. confusion with overall meaning of question as well as misinterpretation of individual terms or concepts Formatting, e.g. problems with how to skip or navigate from question to question may result in missing data and frustration for both interviewers and respondents. Population Individuals Larger units, e.g. families Sometimes Difficult to Specify Population e.g. female faculty members at BC: do we include part-time profs? Samples Must be representative of population. Are the distributions of attributes, opinions, and beliefs in the sample the same as in the population? You want to be able to make inferences about the population as a whole based on what you find to be true of the sample. Often difficult to find representative sample. Always a danger of sampling error or bias. Quality of Sample Important The quality of the sample – whether it is up-to-date and complete – is probably the dominant feature for ensuring adequate coverage of the desired population to be surveyed. Variability Variability is large, then sample should be large Converse also true 2 Barrels of Apples Barrel A (low variability) -- all apples about 3 ins. in diameter (range 3.1 to 2.9 ins.) Barrel B (high variability) -- apples range from 2 to 5 ins. in diameter Picking 3 apples from Barrel B might give result well below (above) average. Size of Sample Isn't Everything Large numbers do not, in and of themselves, increase the representativeness of a sample. Most professional survey conductors hold that a moderate sample size is enough statistically and operationally. Whole Population and Sample Sometimes the Same Example: – Small companies in the paper recycling industry in LA. – Unit of Analysis: a company – You define "small company" as a private co. with turnover of less than $2,000,000 per annum – Research shows that there are 34 relevant companies – Therefore, manageable to use ALL in sample N.B. Results will only relate to small paper recycling companies in LA -- difficult to generalize about other types of company in other parts of the country. Population Often Not Feasible Due to Size • Welfare Recipients • Mentally Ill • Prison Inmates Often essential to survey a REPRESENTATIVE sample. Early Studies of Gay Men Sampling frame composed of men, patients of therapists participating in research But most gay men were not patients of therapists Representative Sample EXAMPLE--Success of unwed teenage mothers in raising children? To be representative, sample must contain same proportion of unwed teenage mothers at --each age level --each educational level --each socio-economic status in community Lists May Be Very Exclusive EXAMPLE Undocumented Aliens --We know that many live in LA --But relying on Govt. lists may be useless Suppose You Have a “Population,” e.g. all registered voters in your county all Mercedes owners in the state all soccer players in your school district who drive green mopeds THEN YOU SELECT SAMPLE IN SUCH A WAY THAT EVERY NAME ON THE LIST HAS AN EQUAL CHANCE OF BEING INCLUDED IN THE SAMPLE Random Sample Random = Purposeful & methodical Not reflect biases of researcher Everyone has equal & independent chance of being selected Random Sample Once selected it cannot be chosen again (like lottery winners) Example: 500 part-time students in Advancing Studies Sample of 20% is required Assign each student a number from 1 to 500 Randomly select 100 numbers (by computer or by table of random numbers) Systematic Random Sampling Example 1. 2,000 in sampling frame and you want a sample of 200, then you might select every 10th name Example 2. 500 part-time students in Advancing Studies Sample of 20% is required --Randomly Select a Number from 1 to 5 --Select Every 5th Person --002, 007, 012. 017, 022, and up to 497. Possible Problem: Staff in govt. agency may be listed unit by unit Each unit has 9 line-level workers and 1 supervisor. The supervisor is the 10th person on the list. It’s a survey of 20% -- every 5th person is selected. If first no. selected is 1, 2, 3, or 4 then no supervisor will be selected, though they comprise 10% of population. If first number selected is 5, then supervisors will be greatly overrepresented. Thus, possibility of bias due to periodicity or patterns. Stratified Sampling Population: 2,000 (800 females; 1,200 males) Sample required: 200 If gender is an important variable in your survey, then both females and males should be included in appropriate numbers, that is, in proportions that correspond to their presence in the population. Strategy: Treat both sexes as separate populations and take 10% sample from each. OR Make sure that all females are listed first and then take every tenth name. Either way you will end up with 80 females and 120 males Convenience Sampling Cluster Sampling Often difficult to list all members of target population and select the sample from among them e.g. 1) Population of American high school students 2) Population of U.S. postal delivery workers 3) Adult population of Atlanta Possible Strategies Population of American high school students choose 50 schools randomly from entire list and include all students in those schools in the sample. Population of U.S. postal delivery workers choose 100 post offices randomly from all 50 States and include all deliverers in those post offices in the sample. Adult population of Atlanta Randomly choose sample of 50 blocks from a city map and then poll all adults living on those blocks. Potential Problems Confidentiality Confidentiality of data supplied by respondents is of prime concern to all reputable survey organizations. Strategies: Using only number codes to link the respondent to a questionnaire. Refusing to divulge names and addresses of survey respondents. Omitting the names and addresses of survey respondents from computer files used for analysis Presenting statistical tabulations by broad enough categories so that individual respondents cannot be singled out. Reporting Important that individual respondents are not identified in reporting survey findings. All of the survey’s results should be presented in totally anonymous summaries, such as statistical tables and charts. Volunteers Volunteers usually have characteristics that differentiate them from the larger population. The fact that they volunteer makes them different from persons in the population who do not volunteer. They tend (but not in all circumstances): – to be better educated – have higher social class – to be more intelligent – have greater need for social approval – to be more sociable – more unconventional (especially when volunteering for studies of sex behavior) – less authoritarian – less conforming Volunteers (Cont.) Jews more likely than Protestants. Protestants more likely than Catholics. Females more likely than males. Volunteers -- Example TV programs asking viewers to vote. – people call who are most committed to issue. – “stuffing of ballots” by multiple calls. – Time of day is important – who’s available? Margin of Error Error margin of 1,000 randomly chosen individuals is said to be 3.1%. Thus, if a random sample of 1,000 indicates that 59% will vote for Bush, the actual number could range from 55.9% to 62.1%. In the 1984 election, the Gallup Survey (using 3,456 individual responses) missed by just +0.2 of 1% when it predicted that Ronald Reagan would win by 59.0%.
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