Sampling and Survey Design

1. Sampling and Survey Design Methods of Sampling Survey Design Types of Surveys

2. Four Types of Nonprobability Sampling Reliance on available subjects Very problematic – focus groups only Purposive or judgmental sampling If Sample frame hard to identify Snowball sampling Good for specialized & linked groups Quota sampling – Deceptively Problematic Quota frames may be inaccurate Selection in frames is not random

3. SRS & Systematic Sampling SRS – Random draw from sampling frame Feasible only with the simplest sampling frame. Systematic Sampling – with random start Computationally much easier Can be more accurate Be careful of arrangement of elements in sampling frame, patterns may result in bias

4. Stratified Sampling Rather than selecting sample for population at large, researcher draws from homogenous subsets of the population. Results in a greater degree of representativeness by decreasing the probable sampling error. Note selection is still random – unlike quota sampling

5. Multistage Cluster & PPS Sampling Clusters of elements selected at random. Then elements chosen at random within clusters. Used when impractical get exhaustive list of the elements in sampling frame. Highly efficient but less accurate PPS (Probability Proportional to Size) Sampling Weights selection of elements by cluster size.

6. Guidelines for Asking Questions Choose appropriate question forms Don’t make form crowded or complex Make items clear Use common sense: how would you answer Pretest, pretest, pretest Keep Survey Short – raise response rate Avoid double-barreled questions Ask for one attitude at a time

7. Guidelines for Asking Questions Give respondents the information they need Be specific in your questions Don’t presume common knowledge Short items are best: one question at a time Avoid negative items and/or biased terms Be aware of question ordering and the flow of the survey Try it out yourself

8. Acceptable Response Rates 50% - adequate for analysis and reporting 60% - good 70% - very good

9. Types of Surveys Self-Administered Mail Survey Now Internet Based as well Face-to-Face Interview Telephone Survey

10. Mail & Internet Surveys Advantages: Inexpensive & logistically easier May tap private or uncomfortable info Can have relatively longer surveys Disadvantages: Lower response rate – make it easy to return Don’t know who is responding Internet has potential for biased return rates

11. Face-to-Face Interviews Advantages: High response rates Can do long surveys & complex items Interviewers gather other data Disadvantages: Very high cost & logistics Possible interviewer effects

12. Telephone Surveys Advantages: Cheaper than face-to-face Higher response rates than mail Very fast results Control over data & who answers Disadvantages: Can’t do long surveys or complex items Still expensive compared to mail