Sample Size

Samples should be as large as a researcher can obtain with a reasonable expenditure of time and energy. A recommended minimum number of subjects is 100 for a descriptive study, 50 for a correctional study and 30 in each group for experimental and causal-comparative studies. Some differences between the sample and the population are bound to exist, but if the sample is randomly selected and of sufficient size, these differences are likely to be relatively insignificant and incidental.

Reflection of a situation: Suppose a target population consists of 1,000 eighth-graders in a given school district. Some samples sizes, of course are obviously too small. Samples with 1 or 2 or 3 individuals, for example, are so small that they cannot possibly be representative. Probably any sample that has less than 20 to 30 individuals is too small, since that would only be 3 or 3 percent of the population. On the other hand, a sample can be too large, given the amount of time and effort the researcher must put into obtaining it. In this example, a sample of 250 or more individuals would probably be needlessly large, as that would constitute a quarter of the population. But what about samples of 50 or 100 or even 200? The question arise is the the size of sample would be too large? The best answer is that a sample should be as large as the researcher can obtain with a reasonable expenditure of time and energy.