A Generalized Negative Binomial Distribution

A generalized negative binomial (GNB) distribution with an additional parameter β has been obtained by using Lagrange’s expansion. The parameter is such that both mean and variance tend to increase or decrease with an increase or decrease in its value but the variance increases or decreases faster than the mean. For β = 1/2, the mean and variance are approximately equal and so the GNB distribution resembles the Poisson distribution. When β = 0 or 1, the GNB distribution reduces to the binomial or negative binomial distribution respectively. It has been shown that the generalized negative binomial distribution converges to a Poisson-type distribution in which the variance may be more or less than the mean, depending upon the value of a parameter. Expected frequencies have been calculated for a number of examples to show that the distribution provides a very satisfactory fit in different practical situations. Its convolution property together with other properties are quite interesting.