1. A computer comprising: a processor; a memory; and a class membership prediction program in the memory, execution of the class membership prediction program by the processor configuring the computer to implement functions, including functions to: for each class of a plurality of classes, calculate a prior probability that a user belongs to the respective class based on sample data of usage and demographic information of users of a product or service, the sample data including an indicator of membership in each class correlated to the data of usage and/or the demographic information; for at least a first predictor of a class of membership in the sample data, calculate a respective first conditional probability that the first predictor is within a first predetermined range or has a first predetermined value given the condition that a user of the product or service is a member of each respective class; for at least a second predictor of the class of membership in the sample data, calculate a respective second conditional probability that the second predictor is within a second predetermined range or has a second predetermined value given the condition that the user of the product or service is a member of each respective class; and for each record of detailed data of usage and demographic information of a plurality of users of the product or service: calculate, for each respective class, a probability of membership that a user corresponding to the record of detailed data is a member of each respective class based on the respective prior probability and the first and second respective conditional probabilities, the record of detailed data not including an indicator of the class of membership; and predict the class of membership of the user corresponding to the record of detailed data by selecting as the class of membership the class with a maximum calculated probability of membership for the record of detailed data.