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
 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) 
