# BETAINV

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Returns the inverse of the cumulative beta probability distribution function. That is, if probability = BETADIST(x,...), then BETAINV(probability,...) = x. The cumulative beta distribution can be used in project planning to model probable completion times given an expected completion time and variability.

Syntax

BETAINV ( probability , alpha , beta ,A,B)

Probability is a probability associated with the beta distribution.

Alpha is a parameter to the distribution.

Beta is a parameter to the distribution.

A is an optional lower bound to the interval of x.

B is an optional upper bound to the interval of x.

Remarks

• If any argument is nonnumeric, BETAINV returns the #VALUE! error value.

• If alpha 0 or beta 0, BETAINV returns the #NUM! error value.

• If probability 0 or probability > 1, BETAINV returns the #NUM! error value.

• If you omit values for A and B, BETAINV uses the standard cumulative beta distribution, so that A = 0 and B = 1.

BETAINV uses an iterative technique for calculating the function. Given a probability value, BETAINV iterates until the result is accurate to within 3x10-7. If BETAINV does not converge after 100 iterations, the function returns the #N/A error value.

Example

Probability

Alpha

Beta

A

B

Formula

Description (Result)

0.685470581

8

10

1

3

=BETAINV([Probability],[Alpha],[Beta],[A],[B])

Inverse of the cumulative beta probability density function for the parameters (2)

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