Basic statistics: Sample size and power: How are sample size and power calculated?

Calculating an appropriate sample size to enable adequate statistical power is critical to planning any research study. A study that has an insufficient sample size and power will be unlikely to yield data that supports a researcher's hypothesis, even when that hypothesis is true. In order to calculate the optimum sample size and power for a study, researchers need to understand the purpose of sample size and power calculations, and important definitions relevant to sample size and power calculations. It is also necessary for researchers to understand what is power and the factors that will influence sample size and power. When and how to calculate sample size and power is another concept that should be considered by the researchers. Sample size and power calculations are estimates of how many participants are needed in a study. An important factor influencing power and sample size is the measurement variance.