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{{Short description|Categorization of data using statistics}}
When [[classification]] is performed by a computer, statistical methods are normally used to develop the algorithm.
Often, the individual observations are analyzed into a set of quantifiable properties, known variously as [[explanatory variables]] or ''features''. These properties may variously be [[categorical data|categorical]] (e.g. "A", "B", "AB" or "O", for [[blood type]]), [[ordinal data|ordinal]] (e.g. "large", "medium" or "small"), [[integer|integer-valued]] (e.g. the number of occurrences of a particular word in an [[email]]) or [[real number|real-valued]] (e.g. a measurement of [[blood pressure]]). Other classifiers work by comparing observations to previous observations by means of a [[similarity function|similarity]] or [[metric (mathematics)|distance]] function.
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==Frequentist procedures==
Early work on statistical classification was undertaken by [[Ronald Fisher|Fisher]],<ref>{{Cite journal |doi = 10.1111/j.1469-1809.1936.tb02137.x|title = The Use of Multiple Measurements in Taxonomic Problems|year = 1936|last1 = Fisher|first1 = R. A.|journal = [[Annals of Eugenics]]|volume = 7|issue = 2|pages = 179–188|hdl = 2440/15227|hdl-access = free}}</ref><ref>{{Cite journal |doi = 10.1111/j.1469-1809.1938.tb02189.x|title = The Statistical Utilization of Multiple Measurements|year = 1938|last1 = Fisher|first1 = R. A.|journal = [[Annals of Eugenics]]|volume = 8|issue = 4|pages = 376–386|hdl = 2440/15232|hdl-access = free}}</ref> in the context of two-group problems, leading to [[Fisher's linear discriminant]] function as the rule for assigning a group to a new observation.<ref name=G1977>Gnanadesikan, R. (1977) ''Methods for Statistical Data Analysis of Multivariate Observations'', Wiley. {{ISBN|0-471-30845-5}} (p. 83–86)</ref> This early work assumed that data-values within each of the two groups had a [[multivariate normal distribution]]. The extension of this same context to more than two
==Bayesian procedures==
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** {{annotated link|Least squares support vector machine}}
Choices between different possible algorithms are frequently made on the basis of quantitative [[Classification#Evaluation of accuracy|evaluation of accuracy]].
==Application domains==
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* {{annotated link|Statistical natural language processing}}
{{More footnotes needed|date=January 2010}}
==See also==
{{Commons category}}▼
{{Portal|Mathematics}}
{{colbegin}}
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==References==
▲{{Commons category}}
{{Reflist}}
{{Statistics|analysis||state=expanded}}
{{Authority control}}
{{DEFAULTSORT:Statistical Classification}}
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