GAMMADIST

Returns the gamma distribution. You can use this function to study variables that may have a skewed distribution. The gamma distribution is commonly used in queuing analysis.

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 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

The example may be easier to understand if you copy it to a blank worksheet.

How to copy an example

1. Create a blank workbook or worksheet.
2. Select the example in the Help topic.

   Note Do not select the row or column headers.

   Selecting an example from Help

3. Press CTRL+C.
4. In the worksheet, select cell A1, and press CTRL+V.
5. To switch between viewing the results and viewing the formulas that return the results, press CTRL+` (grave accent), or on the Formulas tab, in the Formula Auditing group, click the Show Formulas button.

See also:

• CHIDIST
• EXPONDIST
• GAMMAINV
• Statistical functions