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EMR 6500: Survey Research. Dr. Chris L. S. Coryn Kristin A. Hobson Spring 2013. Agenda. Stratified random sampling for means and totals Review. Stratified Random Sampling. Stratified Random Sampling.
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EMR 6500:Survey Research Dr. Chris L. S. Coryn Kristin A. Hobson Spring 2013
Agenda Stratified random sampling for means and totals Review
Stratified Random Sampling Astratified random sample is one in which some form of random sampling is applied in each of a set of separate groups formed from all entries on a sampling frame from which a sample is to be drawn
Strata In stratified random sampling, strata are nonoverlapping groups separating population elements By strategically forming these groups, stratification becomes a feature of the sample design that can improve the statistical quality of survey estimates
Allocation to Strata Deciding how a stratified sample will be distributed among all strata is called stratum allocation The most appropriate allocation method depends on how the stratification will be used
Equal Allocation If the main purpose of stratification is to control subgroup sample sizes for important population subgroups, stratum sample sizes should be sufficient to meet precision requirements for subgroup analysis An important part of the analysis is to produce comparisons among all subgroup strata In this instance, equal allocation (i.e., equal sample sizes) would be appropriate
Proportionate Allocation Proportionate allocation is a prudent choice when the main focus of the analysis is characteristics of several subgroups or the population as a whole and where the appropriate allocations for these analyses are discrepant Proportionate allocation involves applying the same sampling rate to all strata, thus implying that the percent distribution of the selected sample among strata is identical to the corresponding distribution for the population
Optimum Allocation Optimum allocation, in which the most cost-efficient stratum sample sizes are sought, can lead to estimates of overall population characteristics that are statistically superior to those from proportionate allocations When all stratum unit costs are the same, the stratum sampling rates that yield the most precise sample estimates are proportional to the stratum-specific standard deviations (Neyman allocation)
Selecting the Sample Size for Estimating Population Means and Totals
Comparison of Allocation Methods Proportionate Neyman General framework
The Tailored Design Method Uses multiple motivational features in compatible and mutually supportive ways to encourage high quantity and quality of responses
The Tailored Design Method Premised on social exchange perspective on human behavior Assumes that the likelihood of responding is greater when the expected rewards outweigh the anticipated costs
The Tailored Design Method Gives attention to all aspects of contacting and communicating with respondents Encourages response by considering survey sponsorship, the nature of the population and variations within it, and content of questions
The Tailored Design Method Emphasizes reducing errors of coverage, sampling, nonresponse, and measurement
Coverage Error Occurs when all members of a population do not have a known, non-zero probability of selection Occurs when those who are excluded are different from those who are included
Sampling Error Results from surveying only some rather than all members of a population Represented by B, the bound on the error of estimation
Nonresponse Error • Occurs when people selected do not respond and are different than those who do • Nonresponse can occur at the level of items within a survey or at the level of the survey • MAR • MCAR
Measurement Error Occurs when responses are inaccurate or imprecise Primarily related to poor layout and poor design and wording of questions
Social Exchange and Surveys • Addresses three central questions about design and implementation • How can the perceived rewards for responding be increased? • How can the perceived costs of responding be reduced? • How can trust be established so that people believe the rewards will outweigh the costs of responding?
Increasing Benefits Provide information about the survey Ask for help or advise Show positive regard Say thank you Support group values Give tangible rewards Make the questionnaire interesting Provide social validation Inform people that opportunities to respond are limited
Decreasing Costs Make it convenient to respond Avoid subordinating language Make the questionnaire short and easy to complete Minimize requests for personal or sensitive information Emphasize similarity to other requests or tasks to which a person has already responded
Establishing Trust Obtain sponsorship by legitimate authority Provide a token of appreciation in advance Make the task appear important Ensure confidentiality and security of information
Features that can be Tailored • Survey mode • Singular or multiple • Sample design • Type of sample • Number of units sampled • Incentives • Type of incentive • Amount or cost of incentive • Before or after
Features that can be Tailored • Contacts • Number of contacts • Timing of initial and subsequent contacts • Mode of each contact • Whether contacts will be personalized • Sponsorship information • Visual design of each contact • Text or words in each contact
Features that can be Tailored • Additional materials • Whether to provide them at all • Type of materials (e.g., research report) • Visual design of materials • Text or wording of materials
Features that can be Tailored • Questionnaire • Topics included • Length (duration, number of pages/screens, number of questions) • First page or screen • Visual design • Organization and order of questions • Navigation through questionnaire
