Syntax
GAMMAINV(probability, alpha, beta)
| Parameter | Description |
|---|---|
| probability | Parameter of the GAMMAINV function. |
| alpha | Parameter of the GAMMAINV function. |
| beta | Parameter of the GAMMAINV function. |
Examples
95th percentile server response time
Formula
=GAMMAINV(0.95, 2, 0.5)
Returns ~2.996. 95% of server response times fall below about 3 seconds under this gamma model.
Median claim size
Formula
=GAMMAINV(0.5, 3, 1000)
Returns ~2674. The median insurance claim is about $2,674 when claims follow a gamma(3, 1000) distribution.
First quartile
Formula
=GAMMAINV(0.25, 5, 2)
Returns ~6.735. 25% of observations fall below 6.74 in a gamma distribution with shape=5 and scale=2.
Common Errors
#NUM!
Probability must be between 0 and 1 (inclusive). Alpha and beta must be positive.
#VALUE!
Occurs when arguments are non-numeric.
Tips
Use GAMMA.INV instead
GAMMAINV is the compatibility version. GAMMA.INV is the modern replacement with identical functionality.
Check parameter interpretation
Some references use rate (1/scale) instead of scale. Make sure your beta parameter is the scale (mean = alpha * beta), not the rate.
Pair with GAMMADIST for verification
Verify your result: GAMMADIST(GAMMAINV(p, a, b), a, b, TRUE) should return p. This is a useful sanity check.
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