GAMMAINV

See Also

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 nonnumeric, 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.

Show How?

Create a blank workbook or worksheet.
Select the example in the Help topic. 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 Tools menu, point to Formula Auditing, and then click Formula Auditing Mode.

1

2
3
4

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)