# POISSON

## Content

This function returns the Poisson distribution.

## Syntax

`POISSON( nevents, mean, cumulative )`

## Remarks

This function has these arguments:

| Argument | Description |
| -------- | ----------- |
| *nevents* | Number of events Provide an integer, or the value is truncated. The number must be greater than zero. |
| *mean* | Expected numeric value The number must be greater than zero. |
| *cumulative* | Set to TRUE to return the cumulative Poisson probability that the number of random events occurring is between zero and *nevents* inclusive. Set to FALSE to return the Poisson probability mass function that the number of events occurring is exactly *nevents*. |

## Remarks

The cumulative Poisson probability is calculated as follows:

![](https://gcdocumentsitekrblob.blob.core.windows.net/document-site-files/images/8d606653-16a0-474d-b9dc-e2b4d01c2446/images/Func-POISSON-True.png)

The Poisson probability mass function is calculated as follows:

![](https://gcdocumentsitekrblob.blob.core.windows.net/document-site-files/images/8d606653-16a0-474d-b9dc-e2b4d01c2446/images/Func-POISSON-False.png)

where x is the number of events ( *nevents* argument), and mu is the mean ( *mean* argument).

## Data Types

Accepts numeric data for all arguments. Returns numeric data.

## Examples

`POISSON(A3,B4,TRUE)`

`POISSON(R1C2,3,FALSE)`

`POISSON(7,4,TRUE)` gives the result 0.948866384

`POISSON(7,4,FALSE)` gives the result 0.059540363