Density Function. The Gamma distribution has the probability density function:

f(x) = [1/G(c)]*x(c-1) *e(-x)

0 <= x, c > 0

where

G |
(Gamma) is the Gamma function |

c |
is the shape parameter |

e |
is the base of the natural logarithm, sometimes called Euler's e (2.71...) |

G. This field displays the current variate value for the Gamma distribution. When you edit this value (either manually or with the microscrolls), Statistica computes the associated p-value for the specified shape parameter.

p. This field displays the p-value computed from the specified variate value and shape parameter 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 shape parameter.

Shape. Specify here the shape parameter of the distribution, c. If this parameter is changed, then the p-value will be recomputed based on the respective variate value.

Note. This distribution is also sometimes defined to include a scale parameter (see Gamma Distribution). To include a scale parameter in the computations, you can simply rescale x accordingly.