An analysis method is considered that concerns count data with zero truncation, i.e. frequencies of occurrence of an event greater than or equal to 1 are only reported and the frequency of zero occurrence is not available. Relationship between the counts of occurrences of two related events is particularly interested. Such relationship is modeled by a bivariate gamma-Poisson distribution in this paper. To estimate the unknown parameters involved in the model, a simple method based on sample means is proposed. The estimation procedure is applied to some real datasets and interpretations of the results obtained are given. An additional point emphasized in this paper is that the frequency of zero count is not always trusted even the number is reported.
