GAMMADIST function

Syntax

GAMMADIST(x,alpha,beta,cumulative)

The GAMMADIST function syntax has the following arguments:

• X     Required. The value at which you want to evaluate the distribution.

• Alpha     Required. A parameter to the distribution.

• Beta     Required. A parameter to the distribution. If beta = 1, GAMMADIST returns the standard gamma distribution.

• Cumulative     Required. 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 density function.

Remarks

• If x, alpha, or beta is nonnumeric, GAMMADIST returns the #VALUE! error value.

• If x < 0, GAMMADIST returns the #NUM! error value.

• If alpha ≤ 0 or if beta ≤ 0, GAMMADIST returns the #NUM! error value.

• The equation for the gamma probability density function is:

  

  The standard gamma probability density function 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.

Example

Copy the example data in the following table, and paste it in cell A1 of a new Excel worksheet. For formulas to show results, select them, press F2, and then press Enter. If you need to, you can adjust the column widths to see all the data.