Microsoft KB Archive/104583

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Microsoft Knowledge Base

Excel: POISSON() Function Returns #NUM! Error Value

Last reviewed: September 12, 1996
Article ID: Q104583

The information in this article applies to:

• Microsoft Excel for Windows, versions 4.0, 4.0a, 5.0
• Microsoft Excel for the Macintosh, versions 4.0, 5.0

SUMMARY

In Microsoft Excel, the POISSON() function will return a #NUM! error value if the mean argument (the second argument), raised to the power of the x argument (the first argument), exceeds 9.999E+307.

You will also receive a #NUM! error value if the x argument (the first argument) exceeds 170.

MORE INFORMATION

The POISSON() function returns the Poisson probability distribution. You can use this function to predict the number of events over a specific time, such as the number of cars arriving at a toll plaza in one minute.

Microsoft Excel computes the Poisson probability distribution with the following formula,

```   (e^-y) * (y^x)
--------------
(x!)
```

where:

• e is the base of the natural logarithm, or 2.71828182845904
• y is the expected number of successes (the mean)
• x is the number of actual successes (x)

One of the components of the formula is y raised to the power of x (y^x). If this component exceeds 9.999E+307, the maximum possible positive number in Microsoft Excel, you will receive a #NUM! error value.

Another component of the formula computes the factorial of x (x!). If x exceeds 170, the factorial of x will exceed 9.999E+307, resulting in a #NUM! error.

In general, these errors only occur when you use numbers greater than 100 for the mean and x arguments.

REFERENCES

"Function Reference," version 4.0, pages 328-329

 KBCategory: kbusage KBSubcategory: Additional reference words: 5.00 4.00 4.00a statistics THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY. Last reviewed: September 12, 1996 ©1997 Microsoft Corporation. All rights reserved. Legal Notices.