Upper Critical Values of the F Distribution

More specifically, a test statistic is computed with and degrees of freedom, and the result is compared to this table. For a one-sided test, the null hypothesis is rejected when the test statistic is greater than the tabled value. This is demonstrated with the graph of an F distribution with = 10 and = 10. The shaded area of the graph indicates the rejection region at the significance level. Since this is a one-sided test, we have probability in the upper tail of exceeding the critical value and zero in the lower tail. Because the F distribution is asymmetric, a two-sided test requires a set of of tables (not included here) that contain the rejection regions for both the lower and upper tails.

via itl.nist.gov

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