If you were asked to conduct research on the prevalence of infected people in your area, how would you select your sample?. Sample size is always a concern when designing a statistical study. Too large a sample could be a waste of time and money collecting the data. Also, too small a sample may make the conclusions drawn from the data uncertain. The size of a sample required for a particular study is based on three factors.

1. The desired level of confidence.
2. The maximum allowable error, the researcher will tolerate.
3. The variability in the population under study (as measured by the standard deviation).