Determining Sample Size

Perhaps the most frequently asked question concerning
sampling is “What size sample do I need?” The answer to
this question is influenced by a number of factors, including
the purpose of the study, population size, the risk of
selecting a “bad” sample, and the allowable sampling error.
Interested readers may obtain a more detailed discussion
of the purpose of the study and population size in Sampling
the Evidence of Extension Program Impact, PEOD-5 (Israel,
1992). This paper reviews criteria for specifying a sample
size and presents several strategies for determining the
sample size.