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

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.

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

Note   Do not select the row or column headers.

Selecting an example from Help
• Press CTRL+C.
• In the worksheet, select cell A1, and press CTRL+V.
• 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.
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 (.03263913)
=GAMMADIST(A2,A3,A4,TRUE) Cumulative gamma distribution with the terms above (0.068094)

Applies to:
Excel 2007