A statistic is a numerical summary of observed values for a random variable (or variables) in a sample. The term random indicates that the variable's value, and thus its statistic, may differ across samples that are drawn from the same sample population. A statistic is used to estimate a parameter, a numerical summary of a given variable (or variables) in the population.

A statistic is commonly represented with the common alphabet rather than with Greek letters, as is typically the case with a parameter. For example, a statistic such as a standard deviation is represented by s, whereas the corresponding population parameter is represented by σ.

Describing characteristics of a sample variable (or variables) is often called descriptive statistics. Examples include computing the sample's mean or standard ...