GAMMAINV

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.

How to copy an example

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

   Note Do not select the row or column headers.

   Selecting an example from Help

3. Press CTRL+C.
4. In the worksheet, select cell A1, and press CTRL+V.
5. 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.

See also:

• GAMMADIST
• Statistical functions