In this comprehensive article, we will explore the NEGBINOMDIST formula in Excel, which is used to calculate the negative binomial distribution probability. This formula is particularly useful in situations where you need to determine the probability of a certain number of failures occurring before a specified number of successes in a sequence of independent Bernoulli trials. We will cover the syntax, examples, tips and tricks, common mistakes, troubleshooting, and related formulae for the NEGBINOMDIST function.

## NEGBINOMDIST Syntax

The syntax for the NEGBINOMDIST formula in Excel is as follows:

=NEGBINOMDIST(number_f, number_s, probability_s)

Where:

**number_f**(required) – This is the number of failures that occur before the specified number of successes.**number_s**(required) – This is the number of successes that must occur before the experiment is considered complete.**probability_s**(required) – This is the probability of success on any given trial, expressed as a decimal between 0 and 1.

## NEGBINOMDIST Examples

Let’s look at some examples of how to use the NEGBINOMDIST formula in Excel.

**Example 1:** Suppose you are conducting an experiment where you want to determine the probability of getting 3 failures before achieving 5 successes, with a success probability of 0.6 on each trial. To calculate this probability, you would use the following formula:

=NEGBINOMDIST(3, 5, 0.6)

This formula would return the probability of getting 3 failures before 5 successes, given a success probability of 0.6.

**Example 2:** In a manufacturing process, you want to find the probability of having 2 defective items before producing 10 non-defective items, with a probability of 0.95 for producing a non-defective item. To calculate this probability, you would use the following formula:

=NEGBINOMDIST(2, 10, 0.95)

This formula would return the probability of having 2 defective items before producing 10 non-defective items, given a non-defective item probability of 0.95.

## NEGBINOMDIST Tips & Tricks

Here are some tips and tricks to help you effectively use the NEGBINOMDIST formula in Excel:

- Remember that the probability_s parameter must be a decimal value between 0 and 1. If you have a percentage, divide it by 100 to convert it to a decimal.
- Ensure that the number_f and number_s parameters are non-negative integers. The formula will return an error if these values are negative or non-integers.
- Use the NEGBINOMDIST function to model situations where the number of trials is not fixed, and the experiment continues until a certain number of successes are achieved.

## Common Mistakes When Using NEGBINOMDIST

Here are some common mistakes that users make when using the NEGBINOMDIST formula:

- Using a percentage value for the probability_s parameter instead of a decimal value. Remember to divide the percentage by 100 to convert it to a decimal.
- Entering negative values or non-integers for the number_f and number_s parameters. These values must be non-negative integers for the formula to work correctly.
- Confusing the NEGBINOMDIST function with the BINOMDIST function, which calculates the binomial distribution probability for a fixed number of trials. Use NEGBINOMDIST when the experiment continues until a certain number of successes are achieved, and use BINOMDIST when the number of trials is fixed.

## Why Isn’t My NEGBINOMDIST Working?

If your NEGBINOMDIST formula isn’t working, consider the following troubleshooting steps:

- Check that the probability_s parameter is a decimal value between 0 and 1. If you have a percentage, divide it by 100 to convert it to a decimal.
- Ensure that the number_f and number_s parameters are non-negative integers. The formula will return an error if these values are negative or non-integers.
- Verify that you are using the correct function for your situation. If you need to calculate the probability for a fixed number of trials, use the BINOMDIST function instead of NEGBINOMDIST.

## NEGBINOMDIST: Related Formulae

Here are some related formulae that you may find useful when working with the NEGBINOMDIST function:

**BINOMDIST:**This function calculates the binomial distribution probability for a fixed number of trials. Use this function when the number of trials is fixed, and you want to determine the probability of a certain number of successes.**CRITBINOM:**This function calculates the smallest value for which the cumulative binomial distribution is greater than or equal to a specified criterion. It can be used to find the minimum number of trials required to achieve a certain probability.**HYPGEOMDIST:**This function calculates the hypergeometric distribution probability, which is used when sampling is done without replacement from a finite population.**POISSON:**This function calculates the Poisson distribution probability, which is used to model the number of events occurring in a fixed interval of time or space.**EXPONDIST:**This function calculates the exponential distribution probability, which is used to model the time between events in a Poisson process.

In conclusion, the NEGBINOMDIST formula in Excel is a powerful tool for calculating the negative binomial distribution probability in various situations. By understanding its syntax, examples, tips and tricks, common mistakes, troubleshooting steps, and related formulae, you can effectively use the NEGBINOMDIST function to analyze and model real-world scenarios.