What is an adequate sample size? Is bigger always better?
We sample because we cannot obtain data from every possible data point or participant (the entire population). For example, when your doctor tries to diagnose a problem, aren’t you glad he takes a sample of your blood, not all of it? Just as a sample of your blood indicates conditions in your entire bloodstream, survey sampling allows valid inferences about a population. An important mathematical concept, the Central Limit Theorem, states that as sample size increases, the sample distribution approaches a normal distribution. This means that larger samples are better estimators of population effects than smaller samples. And yes, there is a “magic” number at which sample size becomes pretty good for estimating population parameters, especially when determining significant differences between group means. To help you determine sample size, we’ve prepared an Excel® spreadsheet to perform the calculations.
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