In statistics and quantitative research methodology, a sample is a set of data collected and/or selected from a statistical population by a defined procedure. The elements of a sample are known as sample points, sampling units or observations. Sample size determination is the act of choosing the number of observations or replicates to include in a statistical sample. The sample size is an important feature of any empirical study in which the goal is to make inferences about a population from a sample. In practice, the sample size used in a study is determined based on the expense of data collection, and the need to have sufficient statistical power.
This topic covers: Determination of sample size for simple comparative experiments, Determination of sample size to obtain a confidence interval of specified width and Power of a Study.