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XLeratorDB/statistics Documentation

SQL Server POISSON.DIST function


 
Updated: 9 August 2010

Use POISSON to calculate the Poisson distribution. The formula for the probability density function (pdf) is:
 POISSON
 
The formula for the cumulative distribution function (cdf) is:
 POISSON
Where Q(a,x) is the regularized gamma function
Syntax
SELECT [wctStatistics].[wct].[POISSON] (
   <@X, float,>
 ,<@Mean, float,>
 ,<@Cumulative, bit,>)
Arguments
@X
is the number of events. @X is an expression of type float or of a type that can be implicitly converted to float
@Mean
is the arithmetic mean of the distribution. @Mean is an expression of type float or of a type that can be implicitly converted to float
@Cumulative
is a logical value that determines if the probability density function (False, 0) or the cumulative distribution function (True, 1) is being calculated.
Return Types
float
Remarks
·         @X is truncated to zero decimal places.
·         If @X < 0, POISSON returns an error.
·         If @Mean < 0, POISSON returns an error.
Examples

select
wct.POISSON(2,5,'False')

This produces the following result
 
----------------------
0.0842243374885683
 
(1 row(s) affected)
 

select
wct.POISSON(2,5,'True')

This produces the following result
 
----------------------
0.124652019483081
 
(1 row(s) affected)
 

Select
wct.GAMMAQ(3, 5)

This produces the following result
 
----------------------
0.124652019483081
 

(1 row(s) affected)



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