Syntax
BETA.INV(probability, alpha, beta, [A], [B])
| Parameter | Description |
|---|---|
| probability | Parameter of the BETA.INV function. |
| alpha | Parameter of the BETA.INV function. |
| beta | Parameter of the BETA.INV function. |
| [A] | (Optional.) Parameter of the BETA.INV function. |
| [B] | (Optional.) Parameter of the BETA.INV function. |
Examples
Lower bound of conversion rate
Formula
=BETA.INV(0.05, 12, 88)
Returns ~0.0670. With 11 conversions out of 99 visitors, the 5th percentile of the posterior beta distribution is about 6.7% — a conservative lower bound for the true rate.
PERT pessimistic estimate
Formula
=BETA.INV(0.9, 2, 3, 5, 20)
Returns ~14.94. In a PERT analysis bounded between 5 and 20 days, there is a 90% chance the task completes within about 15 days.
Median of a beta distribution
Formula
=BETA.INV(0.5, 5, 5)
Returns 0.5. A symmetric beta distribution (alpha=beta) always has its median at 0.5.
Common Errors
#NUM!
Probability must be between 0 and 1 (inclusive). Alpha and beta must be positive. If A >= B (custom bounds), this error occurs.
#VALUE!
Occurs when arguments are non-numeric.
Tips
Credible intervals for A/B tests
Use BETA.INV(0.025, s+1, f+1) and BETA.INV(0.975, s+1, f+1) to construct a 95% credible interval for your conversion rate after s successes and f failures.
Optional bounds
The optional A and B parameters let you map the beta distribution to any interval. BETA.INV(p, alpha, beta, A, B) returns a value between A and B.
Inverse of BETA.DIST
BETA.INV(BETA.DIST(x, a, b, TRUE), a, b) = x. Use them together to convert between values and probabilities.
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