statistic

In statistics, a statistic is a numerical summary of a sample. It is a function of the observed data, such as the mean of a set of measurements or the proportion of successes in a trial. A statistic estimates a population parameter, the corresponding fixed quantity for the entire group. Because it depends on the sample, a statistic is a random variable that can vary from one sample to another.

The term statistic also denotes the science that develops and applies methods for collecting, organizing, analyzing and interpreting data. Statistics grew from practical needs in commerce, astronomy and governance and became a formal discipline with standardized concepts and procedures in the 18th through 20th centuries.

Statistics is commonly divided into descriptive statistics, which summarize data, and inferential statistics, which attempt to generalize findings to a population. Common measures include central tendency (mean, median, mode) and dispersion (variance, standard deviation, range, interquartile range). Data types—nominal, ordinal, interval and ratio—shape the choice of analyses.

In inference, a statistic serves as an estimator of a population parameter. Desirable properties include low bias and low variance. Analysts use sampling distributions to assess uncertainty, construct confidence intervals, and perform hypothesis tests and regression analyses.