Sample Size

In clinical psychology, researchers typically want to make inferences at the population level. Because it often is not feasible to study all individuals of a population, a smaller sample of that population is selected. Using statistical inference on that sample, the researcher can investigate phenomena in a sample that generalize to the larger population of interest (e.g., a researcher can make inferences about the mean number of hours of sleep in the population of people with major depression based on a sample of people with major depression). In general, as the number of individuals in that sample increases, the estimates of characteristics become more precise—that is, the confidence interval around that estimate shrinks.

In general, the larger the sample size, the better. However, the number of ...