Negbinomdist function

This article describes the formula syntax and usage of the NEGBINOMDIST function in Microsoft Excel.

Description

Returns the negative binomial distribution. NEGBINOMDIST returns the probability that there will be number_f failures before the number_s-th success, when the constant probability of a success is probability_s. This function is similar to the binomial distribution, except that the number of successes is fixed, and the number of trials is variable. Like the binomial, trials are assumed to be independent.

For example, you need to find 10 people with excellent reflexes, and you know the probability that a candidate has these qualifications is 0.3. NEGBINOMDIST calculates the probability that you will interview a certain number of unqualified candidates before finding all 10 qualified candidates.

Important: This function has been replaced with one or more new functions that may provide improved accuracy and whose names better reflect their usage. Although this function is still available for backward compatibility, you should consider using the new functions from now on, because this function may not be available in future versions of Excel.

For more information about the new function, see NEGBINOM.DIST function.

Syntax

NEGBINOMDIST(number_f,number_s,probability_s)

The NEGBINOMDIST function syntax has the following arguments:

• Number_f     Required. The number of failures.

• Number_s     Required. The threshold number of successes.

• Probability_s     Required. The probability of a success.

Remarks

• Number_f and number_s are truncated to integers.

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

• If probability_s < 0 or if probability > 1, NEGBINOMDIST returns the #NUM! error value.

• If number_f < 0 or number_s < 1, NEGBINOMDIST returns the #NUM! error value.

• The equation for the negative binomial distribution is:

  

  where:

  x is number_f, r is number_s, and p is probability_s.

Example

Copy the example data in the following table, and paste it in cell A1 of a new Excel worksheet. For formulas to show results, select them, press F2, and then press Enter. If you need to, you can adjust the column widths to see all the data.

Data	Description
10	Number of failures
5	Threshold number of successes
0.25	Probability of a success
Formula	Description	Result
=NEGBINOMDIST(A2,A3,A4)	Negative binomial distribution for the terms above.	0.05504866