Sample Size
Statistical hypothesis testing involves performing the same experiment on multiple subjects. The number of subjects is known as the sample size. The properties of the procedure depends on the sample size. Even if a null hypothesis does not hold for the population, an insufficient sample size may prevent its rejection. If sample size is under a researcher's control, a good choice depends on the statistical power of the test, the effect size that the test must reveal and the desired significance level. The significance level is the probability of rejecting the null hypothesis when the null hypothesis holds in the population. The statistical power is the probability of rejecting the null hypothesis when it does not hold in the population (i.e., for a particular effect size).
Read more about this topic: Null Hypothesis
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