Syntax. GAMMA.INV(probability,alpha,beta)
Definition. This function returns the quantile of the gamma distribution. If p = GAMMA.DIST(x,...) then GAMMA.INV(p,...) = x.
Use this function to examine a variable whose distribution may be skewed.
Arguments
probability (required). A probability associated with the gamma distribution.
alpha (required). A parameter of the distribution.
beta (required). A parameter of the distribution. If beta = 1, GAMMA.INV() returns the standard gamma distribution.
Note
If one of the arguments isn’t a numeric expression, the GAMMA.INV() function returns the #VALUE! error.
If probability is less than 0 or greater than 1, the GAMMA.INV() function returns the #NUM! error.
If alpha or beta is less than or equal to 0, the GAMMA.INV() function returns the #NUM! error.
If probability has a value, GAMMA.INV() looks for the value x so that GAMMA.DIST(x, alpha, beta, TRUE) = probability. Therefore, the accuracy of GAMMA.INV() depends on the accuracy of GAMMA.DIST(). GAMMA.INV() uses an iterative search technique. If the search has not converged after 100 iterations, the function returns the #N/A error.
Background. GAMMA.INV() is the inverse function of GAMMA.DIST() and can be used to monitor a gamma distribution. The alpha and beta arguments correspond to the values for the GAMMA.DIST() function. The probability can be any value from 0 through 100 percent. GAMMA.INV() calculates the position of x on the horizontal axis that matches the cumulative area ratio of the gamma distribution.
See Also
You will find more information about gamma distributions in the description of GAMMA.DIST().
Example. Use the values in Figure 12-65 to calculate GAMMA.INV(). The figure also shows the calculation of GAMMA.INV().
The GAMMA.INV() function returns the quantile 10 for the gamma distribution based on the parameters shown.