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Sampling

Sampling. Sampling relates to the degree to which those surveyed are representative of a specific population The sample frame is the set of people who have the chance to respond to the survey

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Sampling

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  1. Sampling • Sampling relates to the degree to which those surveyed are representative of a specific population • The sample frame is the set of people who have the chance to respond to the survey • A question related to external validity is the degree to which the sample frame corresponds to the population to which the researcher wants to apply the results (Fowler, 1988)

  2. Sampling • Two basic types: probability and non-probability • Probability sampling can include random sampling, stratified random sampling, and cluster sampling • Non-probability sampling can include quota sampling, haphazard sampling, and convenience sampling

  3. Random Sampling • Every unit has an equal chance of selection • Although it is relatively simple, members of specific subgroups may not be included in appropriate proportions

  4. Stratified Random Sampling • The population is grouped according to meaningful characteristics or strata • This method is more likely to reflect the general population, and subgroup analysis is possible • However, it can be time consuming and costly

  5. Systematic Sampling • Every xth unit is selected • The method is convenient and close to random sampling if the starting point is randomly chosen • Recurring patterns can occur and should be examined

  6. Cluster/Multistage Sampling • Natural groups are sampled and then their members are sampled • This method is convenient and can use existing units

  7. Convenience Sampling • This method uses readily available groups or units of individuals • It is practical and easy to use • However, it may produce a biased sample • Convenience sampling can be perfectly acceptable if the purpose of the research is to test a hypothesis that certain variables are related to one another

  8. Snowball Sampling • Previously identified members identify others • This method is useful when a list of potential names is difficult to obtain • However, it may produce a biased sample

  9. Quota Sampling • The population is divided into subgroups and the sample is selected based on the proportions of the subgroups necessary to represent the population • This method depends on reliable data about the proportions in the population

  10. Response Rates • Whatever the sampling technique, response rates and non-response bias must be considered • Lowered response rates introduce bias into the sample • In cases of low response rates, people who respond to the survey are likely to be systematically different from people who do not respond to the sample

  11. Response Rates • In mail surveys, the results of non-response bias can be examined by comparing those who respond early with those who respond after follow up • Most government-sponsored surveys require response rates of 75% • For mail surveys, post-cards, follow-up letters, and telephone calls are used to increase the response rates (Fowler, 1988) • According to Babbie (1989), a response rate of 70% is very good, 60% is good, and 50% is adequate

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