Standard error (SE) is a statistic that reveals how accurately sample data represents the whole population. It measures the accuracy with which a sample distribution represents a population. In statistics, a sample mean deviates from the actual mean of a population; this deviation is the standard error of the mean.

The standard error is considered part of inferential statistics—or, the conclusions drawn from the study. It is inversely proportional to the sample size; the larger the sample size, the smaller the standard error because the statistic will approach the actual value.