Explain how to evaluate the quality of a sample.
What will be an ideal response?
• We cannot evaluate the quality of a sample if we do not know what population it is supposed to represent. If the population is unspecified because the researchers were never clear about just what population they were trying to sample, then we can safely conclude that the sample itself is no good.
• We cannot evaluate the quality of a sample if we do not know exactly how cases in the sample were selected from the population. If the method was specified, we then need to know whether cases were selected in a systematic fashion or on the basis of chance. In any case, we know that a haphazard method of sampling (as in person-on-the-street interviews) undermines generalizability.
• Sample quality is determined by the sample actually obtained, not just by the sampling method itself. That is, findings are only as generalizable as the sample from which they are drawn. If many of the people (or other elements) selected for our sample do not respond or participate in the study, even though they have been selected for the sample, generalizability is compromised.
• We need to be aware that even researchers who obtain very good samples may talk about the implications of their findings for some group that is larger than or just different from the population they actually sampled. For example, findings from a representative sample of students in one university often are discussed as if they tell us about university students in general. Maybe they do; the problem is, we just don’t know.
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