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Mean of Geometric and Negative Binomial distributions


Dear Group,

Can anyone tell me why Mathematica returns (1-p)/p for
Mean[GeometricDistribution[p]] and n(1-p)/p for
Mean[NegativeBinomialDistribution[p]], when all sources I have to hand (such
as CRC Standard Mathematical Formulae) give these as 1/p and n/p
respectively?

The variance expressions agree with CRC, it's just the means that are
different.

Thanks,

Gareth
 
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Dr. Gareth J. Russell

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Center for Environmental Research and Conservation
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OLD ADDRESS (AND STILL MY EMPLOYERS)

Department of Ecology and Evolutionary Biology
  University of Tennessee
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