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Statistic
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<p>A statistic (singular) or sample statistic is any quantity computed from values in a <a href="/facts/Sample_(statistics)/URCwKNge">sample</a> which is considered for a statistical purpose. Statistical purposes include <a href="/facts/Estimation/dsztTYcy">estimating</a> a <a href="/facts/Statistical_population/KAILs8E3">population</a> parameter, describing a sample, or evaluating a hypothesis. The <a href="/facts/Arithmetic_mean/L3Pv333o">average (or mean)</a> of sample values is a statistic. The term statistic is used both for the function (e.g., a calculation method of the average) and for the value of the function on a given sample (e.g., the result of the average calculation). When a statistic is being used for a specific purpose, it may be referred to by a name indicating its purpose. </p><p>When a statistic is used for estimating a population parameter, the statistic is called an <i><a href="/facts/Estimator/CbkjcKvN">estimator</a></i>. A population parameter is any characteristic of a population under study, but when it is not feasible to directly measure the value of a population parameter, statistical methods are used to infer the likely value of the parameter on the basis of a statistic computed from a sample taken from the population. For example, the <a href="/facts/Sample_mean/Ah8VVVDT">sample mean</a> is an <a href="/facts/Bias_of_an_estimator/oxIvEgmd">unbiased estimator</a> of the <a href="/facts/Population_mean/swcEd4Pg">population mean</a>. This means that the <a href="/facts/Expected_value/1XV0JKL8">expected value</a> of the sample mean equals the true population mean. </p><p>A <i><a href="/facts/Descriptive_statistic/vnTP8Ryr">descriptive statistic</a></i> is used to summarize the sample data. A <i><a href="/facts/Test_statistic/IBwfN5Kx">test statistic</a></i> is used in <a href="/facts/Statistical_hypothesis_testing/yv9RPF6U">statistical hypothesis testing</a>. A single statistic can be used for multiple purposes – for example, the sample mean can be used to estimate the population mean, to describe a sample data set, or to test a hypothesis. </p>