COMPoissonReg: Usage, the Normalizing Constant, and Other Computational Details

I have been maintaining the COMPoissonReg package, which facilitates use of the Conway-Maxwell Poisson (CMP) distribution. The normalizing constant of the CMP distribution is central to many computations in the package. Users have occasionally reported strange results that can be traced back to problems computing the normalizing constant. Early versions computed the constant by truncating the series to an finite sum with a fixed number of terms; however, this may yield inaccurate results. We addressed this to some degree in more recent versions in an ad hoc way. In the latest version (0.8.0) of the package, these computations have been revisited in a more principled way. Kimberly Sellers and I recently completed a report describing the updated method, which also demonstrates general use of the package. A vignette version of this report will be included in the package and updated along with any changes in the software.