## Probability Distribution Functions

(Revised 2014-07-29: provide fairly good approximate results for fractional degrees of freedom

This screen computes the probability distribution functions and their inverses for four common statistical distributions.

Note: Before using this page for the first time, make sure you read the JavaStat user interface guidelines for important information about interacting with JavaStat pages.

Caution: This page gives completely accurate results when the degrees of freedom (d.f.) are whole numbers, but only approximate results for fractional d.f. The approximations are usually good to at least 2 or 3 decimal places, even for very small d.f., and get better for larger d.f.

## Normal (Gaussian)

 z p

Note: p is the area in the two tails of the distribution

## Student t

 t d.f. p

Note: p is the area in the two tails of the distribution

## Chi Square

 ChiSq d.f. p

Note: p is a "one-tailed" area (from ChiSq to infinity)

## Fisher F

 F d.f.1 (num) d.f.2 (denom) p

Note: p is a "one-tailed" area (from F to infinity)