Functions and CALL Routines 
Returns the probability from a Poisson distribution.

m

is a numeric mean parameter.
Range: 
m 0 

n

is an integer random variable.
Range: 
n 0 
The POISSON function returns the probability
that an observation from a Poisson distribution, with mean m,
is less than or equal to n. To compute the probability that an
observation is equal to a given value, n, compute the difference
of two probabilities from the Poisson distribution for n and n1.
SAS Statements 
Results 
x=poisson(1,2);

0.9196986029

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