1. Introduction
In many applications, the variable of interest is given in the form of an event count or a non-negative integer value which refers to the number of a occurrences of particular phenomenon over a fixed set of time, distance, area or space. Some examples of such data are number of road accident victims per week, number of cases with a specific disease in epidemiology, etc. Poisson distribu- tion is a standard and good model for analyzing count data and it seems to be the most common and frequently used as well.