# GAMMAINV function

Returns the inverse of the gamma cumulative distribution. If p = GAMMADIST(x,...), then GAMMAINV(p,...) = x.

You can use this function to study a variable whose distribution may be skewed.

Syntax

GAMMAINV(probability,alpha,beta)

Probability     is the probability associated with the gamma distribution.

Alpha     is a parameter to the distribution.

Beta     is a parameter to the distribution. If beta = 1, GAMMAINV returns the standard gamma distribution.

Remarks

• If any argument is text, GAMMAINV returns the #VALUE! error value.
• If probability < 0 or probability > 1, GAMMAINV returns the #NUM! error value.
• If alpha ≤ 0 or if beta ≤ 0, GAMMAINV returns the #NUM! error value.

Given a value for probability, GAMMAINV seeks that value x such that GAMMADIST(x, alpha, beta, TRUE) = probability. Thus, precision of GAMMAINV depends on precision of GAMMADIST. GAMMAINV uses an iterative search technique. If the search has not converged after 100 iterations, the function returns the #N/A error value.

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
0.068094 Probability associated with the gamma distribution
9 Alpha parameter to the distribution
2 Beta parameter to the distribution
Formula Description (Result)
=GAMMAINV(A2,A3,A4) Inverse of the gamma cumulative distribution for the above terms (10.00001131)

Applies to:
Excel 2007