GAMMADIST

Description: Returns the gamma distribution. You can use this function to study variables that may have a skewed distribution.

Syntax: GAMMADIST(x, Alpha, Beta, Cumulative)

  • x is the value at which you want to evaluate the distribution.
  • Alpha is a parameter to the distribution.
  • Beta is a parameter to the distribution. If Beta = 1, GAMMADIST returns the standard gamma distribution.
  • Cumulative is a logical value that determines the form of the function. If Cumulative is TRUE, GAMMADIST returns the cumulative distribution function; if FALSE, it returns the probability mass function.

Remarks:

  • x, alpha and beta must be numerical.
  • x must be >= 0.
  • Alpha and Beta must be > 0.
  • The equation for the gamma distribution is:

  • The standard gamma distribution is:

  • When Alpha = 1, GAMMADIST returns the exponential distribution with:

  • For a positive integer n, when Alpha = n/2, Beta = 2, and Cumulative = TRUE, GAMMADIST returns (1 - CHIDIST(x)) with n degrees of freedom.
  • When Alpha is a positive integer, GAMMADIST is also known as the Erlang distribution.
  • When used in an event analysis flowchart, the x, Alpha and Beta parameters must evaluate to numerical values. They can include:

Example:

  • GAMMADIST(10,9,2,FALSE) = 0.032639
  • GAMMADIST(10,9,2,TRUE) = 0.068094

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