GAMMADIST function

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.

 Important   This function has been replaced with one or more new functions that may provide improved accuracy and whose names better reflect their usage. Although this function is still available for backward compatibility, you should consider using the new functions from now on, because this function may not be available in future versions of Excel.

For more information about the new function, see GAMMA.DIST function.

Syntax

GAMMADIST(x,alpha,beta,cumulative)

The GAMMADIST function syntax has the following arguments (argument: A value that provides information to an action, an event, a method, a property, a function, or a procedure.):

  • 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:

Equation

The standard gamma probability density function is:

Equation

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

Equation

  • 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.

ShowHow do I copy an example?

  1. Select the example in this article. If you are copying the example in Excel Web App, copy and paste one cell at a time.Important Do not select the row or column headers.

Selecting an example from Help

Selecting an example from Help

  1. Press CTRL+C.
  2. Create a blank workbook or worksheet.
  3. In the worksheet, select cell A1, and press CTRL+V. If you are working in Excel Web App, repeat copying and pasting for each cell in the example.

Important For the example to work properly, you must paste it into cell A1 of the worksheet.

  1. 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.

After you copy the example to a blank worksheet, you can adapt it to suit your needs.

 
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A B
Data Description
10.00001131 Value at which you want to evaluate the distribution
9 Alpha parameter to the distribution
2 Beta parameter to the distribution
Formula Description (Result)
=GAMMADIST(A2,A3,A4,FALSE) Probability gamma distribution with the terms above (0.032639)
=GAMMADIST(A2,A3,A4,TRUE) Cumulative gamma distribution with the terms above (0.068094)
 
 
Applies to:
Excel 2010, Excel Web App, SharePoint Online for enterprises, SharePoint Online for professionals and small businesses