Buy Till you Die  The Buy Till You Die (BTYD) class of statistical models are designed to capture the behavioral characteristics of non-contractual customers, or when the company is not able to directly observe when a customer stops being a customer of a brand. The goal is typically to model and forecast customer lifetime value. BTYD models all jointly model two processes: (1) a repeat purchase process, that explains how frequently customers make purchases while they are still "alive"; and (2) a dropout process, which models how likely a customer is to churn in any given time period. Common versions of the BTYD model include:   The concept was firstly introduced in 1987, in an article in Management Science, which concerns on counting and identifying those customers who are still active.