The Finite Population Correction Factor, sometimes just called the FPC factor, is used when the sample size is large relative to the population size. For most situations, the population is so large, typical sample sizes are far too small to worry about the need for the FPC.

The guidance is that we need to use the FPC when the ratio of the sample size n to the population size N is greater than 5%. For example, if the population size is 300 and the sample size is 30, we have a ratio of 10% and thus need to use the FPCF.

The most common formula for calculating the FPC isFinite Population Correction factor