This article corrects two errors in the study by Banerjee and Bhattacharyya. It shows that the mixture of inverse Gaussian distributions provides a better fit to the purchase frequencies than implied by Banerjee and Bhattacharyya's work. Link to the article
BEMMAOR, A.C. and HOPPE, D. (2008). On Banerjee and Bhattacharyya (1976), "A Purchase Incidence Model with Inverse Gaussian Interpurchase Times," Journal of the American Statistical Association, 71, 823-829. Journal of the American Statistical Association, 103(482), pp. 894-895.