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In comparing two independent samples of size *N*_{1} and *N*_{2} the F Test provides a measure for the probability that they have the same variance. The estimators of the variance are *s*_{1}^{2}
and *s*_{2}^{2}.
We define as test statistic their ratio *T* = *s*_{1}^{2}/ *s*_{2}^{2},
which follows an F Distribution with *f*_{1}= *N*_{1}-1 and *f*_{2}= *N*_{2}-1 degrees of freedom. One can formulate the F test for three different hypotheses, defined by:

Tables of the quantiles , etc., of the F distribution can be found in the literature (e.g. [Brandt83]).

Rudolf K. Bock, 7 April 1998