Rainer Winkelmann, Curtis S. Signorino, and Gary King. "A Correction for an Underdispersed Event Count Probability Distribution," Political Analysis, (1995): Pp. 215-228, copy at http://gking.harvard.edu/files/abs/correction-abs.shtml.. (Article: PDF)

Abstract

We demonstrate that the expected value and variance commonly given for a well-known probability distribution are incorrect. We also provide corrected versions and report changes in a computer program to account for the known practical uses of this distribution.

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