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In comparing two independent samples of size ''N''<sub>1</sub> and ''N''<sub>2</sub> the F Test provides a measure for the probability that they have the same variance. The estimators of the variance are ''s''<sub>1</sub><sup>2</sup> and ''s''<sub>2</sub><sup>2</sup>. We define as test statistic their ratio ''T'' = ''s''<sub>1</sub><sup>2</sup>/ ''s''<sub>2</sub><sup>2</sup>, which follows an [[F distribution#79|F Distribution]] with ''f''<sub>1</sub>= ''N''<sub>1</sub>-1 and ''f''<sub>2</sub>= ''N''<sub>2</sub>-1 degrees of freedom. One can formulate the F test for three different hypotheses, defined by:

[[File:hepa_img326.gif|303x70px]]

Tables of the quantiles [[File:hepa_img327.gif|18x23px]] , etc., of the F distribution can be found in the literature (e.g. [[References 1#bran83|Brandt83]]).

[[Category:W.Krisher and R.Bock]]
[[Category:Data analysis]]
[[Category:Statistics]]

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