The number of entities (subjects and so on) in a subset of a population selected for analysis. The size of the sample and the way in which it has been drawn from the population are critical issues on any research study. For some, such as clinical trials, particularly where one wants the sample to be representative of the population, size is a major indicator of the statistical power of the analysis. Randomization in the sample selection is usually necessary for statistical tests to be valid. In other cases, however, as is sometimes the practice in qualitative studies, samples will be taken in order to reveal other attributes of the population that need not be representative.
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