# Statistical parameter

## Quantity that indexes a parametrized family of probability distributions / From Wikipedia, the free encyclopedia

In statistics, as opposed to its general use in mathematics, a **parameter** is any quantity of a statistical population that summarizes or describes an aspect of the population, such as a mean or a standard deviation. If a population exactly follows a known and defined distribution, for example the normal distribution, then a small set of parameters can be measured which completely describes the population, and can be considered to define a probability distribution for the purposes of extracting samples from this population.

A "parameter" is to a population as a "statistic" is to a sample; that is to say, a parameter describes the **true value** calculated from the full population (such as the population mean), whereas a statistic is an estimated measurement of the parameter based on a sample (such as the sample mean). Thus a "statistical parameter" can be more specifically referred to as a **population parameter**.^{[1]}^{[2]}