Sample Size

Sample size in the context of educational research refers to the number of participants in an experiment or study. The sample size has implications for how accurate the estimate of the effect under study will be (precision) as well as how detectable the effect will be (statistical power). This entry discusses the role sample size plays in both precision and power as well as how to plan the appropriate sample size for an educational study.


To understand how sample size is involved in the accuracy of an effect, consider a basic political poll. Suppose that 20 individuals sampled at random were interviewed about their choice between two different candidates. This type of study is modeled with the binomial distribution. If 12 of the 20 individuals reported ...

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