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From: John O
Remote Name: 149.159.81.206
Date: 10 Mar 2005
Time: 18:48:45 -0700
Does anyone know what the expected value of the negative binomial distribution is? Originally I thought it was: r(1-p)/p but then I was reading "A first year in prob" by Sheldon and it said that the expected value was r/p. That made more sense because the negative is just like the geometric and the expected value of the geometric is 1/p. B/c the trials are all independent, just r/p made sense. But then I noticed several other books had r(1-p)/p. So I began to think maybe it was a typo in Sheldon. But then I saw there was a proof that it was r/p in sheldon. But then I found a website on the internet that also had a proof that it was equal to r(1-p)/p. They both looked legitimate. How can this be? Which is the real expected value of the negative binomial? Thanks, John