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 Microsoft Excel > Functions > Statistical > POISSON
 

POISSON(x, mean, cumulative)

 
 Returns the Poisson distribution. A common application of the Poisson distribution is predicting the number of events over a specific time, such as the number of cars arriving at a toll plaza in 1 minute.

 xThe number of events.
 meanThe expected numeric value.
 cumulativeTrue or False to specify the type of probability distribution used.

 REMARKS
 
  		• If "x" is not an integer, it is truncated.
     
  		• If "x" is not numeric, then #VALUE! is returned.
     
  		• If "mean" is not numeric, then #VALUE! is returned.
     
  		• If "mean" = 0, then #NUM! is returned.
     
  		• If "cumulative" = True, then the cumulative Poisson probability function is used.
     
  		• If "cumulative" = False, then the Poisson probability mass function is used.
     
  		• The cumulative Poisson probability function says that the number of random events occurring will be between zero and "x".
     
  		• The Poisson probability mass function says that the number of random events occurring will be exactly "x".
     
  		• If "x" = 0, then #NUM! is returned.
     
  		• The accuracy of this function was improved in Excel 2003. For more information please refer to this Knowledge Base Article (828130).

     EXAMPLES
     
     A
    1=POISSON(2,5,FALSE) = 0.084
    2=POISSON(2,5,TRUE) = 0.125
    3=POISSON(2,2,1) = 0.677
    4=POISSON(-2,2,1) = #NUM!
    		 
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