Density Function. The F distribution (for x > 0) has the probability density function (for n = 1, 2, ...; w = 1, 2, ...):

f(x) = [G{(n+w)/2}]/[G(n/2)G(w/2)] * (n/w)(n/2) * x[(n/2)-1] * {1+[(n/w)*x]}[-(n+w)/2]

where

n, w |
are the shape parameters, degrees of freedom |

G |
is the Gamma function |

F. This field displays the current variate value for the F distribution. When you edit this value (either manually or with the microscrolls), Statistica computes the associated p-value for the specified degrees of freedom.

p. This field displays the p-value computed from the specified variate value and degrees of freedom or you can enter a desired p-value (either manually or edit the existing value with the microscrolls) and compute the critical value of the distribution for the specified degrees of freedom.

df1, df2. Specify here the shape parameters of the distribution, n and w, respectively. If one or both of these parameters are changed, then the p-value will be recomputed based on the respective variate value.