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8. Quota sampling involves the selection of a certain percentage of individuals from specified subgroups
of the population when the population is large and lists of members are not available. Many polling

organizations use this technique.
9. Appropriate sample size depends on various considerations, including population variability,
statistical issues, economic factors, and availability of participants. In general, with larger samples

you will have a smaller margin of error and you can detect smaller differences.
10. The larger the variability of scores in the population, the larger the sample must be in order to be

representative.
11. Sampling error includes systematic error and random error. Systematic error occurs when the sample
is not properly drawn (an error of the researcher). Random error is the degree to which the sample is

not perfectly representative of the population. Even with the best sampling techniques, some degree
of random error is expected.
12. Increasingly, we are exposed to information based on sample data. Understanding the principles of

sampling, particularly the limitations of various methods, should make us more critical consumers of
such information.

Key Terms
census

confidence interval
convenience sampling

element
exhaustive list
nonprobability sampling

population
probability sampling

quota sampling
random sampling
random sampling error

sample
sampling error
stratified random sample

systematic sampling error