1. A computer-implemented method for developing an advertiser-specific behavioral lift model, the method executed by a computer system and comprising: maintaining in the computer system a plurality of user profiles, each user profile including a persistent identifier of a user and a plurality of user behavior vectors for the user, the user behavior vectors indicating occurrences of each of a set of behaviors by the user, each occurrence having a date; receiving, by the computer system, conversion information relating to a plurality of advertisers associated with the plurality of user profiles, the conversion information indicating users' responses to an advertisement of the advertiser, the users' responses associated with user profiles; and calculating by the computer system a lift model for each advertiser based upon the user behavioral vectors wherein the lift model for each advertiser identifies a sequence of advertiser behavior tuples with respect to that advertiser; and wherein each advertiser behavior tuple of the sequence of advertiser behavior tuples is associated with a lift for an population of user profiles which do not exhibit any behaviors corresponding to advertiser behavior tuples previously indicated in the sequence of advertiser behavior tuples; wherein the associated lift for the advertiser behavior tuples in the sequence generally decreases through the sequence.