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:

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

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Selecting an example from Help

Selecting an example from Help
  • Press CTRL+C.
  • In the worksheet, select cell A1, and press CTRL+V.
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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 (.03263913)
=GAMMADIST(A2,A3,A4,TRUE) Cumulative gamma distribution with the terms above (0.068094)
 
 
Applies to:
Excel 2003