P-Value Calculator

This returns the p-value for a t statistic or an F statistic you already have, from a t-test, a regression coefficient or an ANOVA table. You enter the statistic, its degrees of freedom and which tail you want, and it returns that p-value together with the other tails and a comparison against a significance level you choose. PHP has no distribution functions, so the tail is worked out from the regularised incomplete beta function by a continued fraction rather than read off a table, and the result says which formula it used. The z and chi-square cases already have their own pages here, so this one covers the two they do not.

Calculator Type

For a t statistic you already have, from a t-test, a regression coefficient or a printout. Fractional degrees of freedom are accepted, which is what a Welch test gives.

T Statistic *

A negative t is fine. For a two-tailed p only the size matters.

Degrees of Freedom *

Tail

Significance Level Alpha (optional)

Only used for the comparison line. It does not change the p-value.

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