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)

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Send e-mail to John C. Pezzullo at statpages.org@gmail.com