1. A method to be used by or for an entity which transacts with customers to provide the customers with goods or services, and which records attributes of customer transactions, referred to as profile variables, comprising at least one of time or duration of a transaction, nature or amount of the thing contracted for, or other transactional attributes having two or more possible values and lending themselves to treatment as statistical variables, for the purpose of distinguishing customers by their records of transactional behavior, the method comprising: a) from a new transaction with a customer, obtaining at least one new value of a profile variable and storing said value in a computer-accessible medium; b) from the new transaction, obtaining a corresponding value of at least one additional variable selected to have some discriminating power for most customers and more discriminating power for at least a specified fraction of the population of customers, the additional variable being referred to as a stratification variable; c) assigning the obtained value of at least one said stratification variable to one stratum from a plurality of strata, wherein each said stratum corresponds to a distinct value or range of values of the stratification variable; d) assigning the obtained value of a profile variable to one of a plurality of bins which represent respective ranges of possible values of the profile variable; e) accessing, using a computer, a storage medium containing one or more histograms for each customer in the customer population, wherein: each histogram represents a relative frequency with which values of a profile variable for a given individual customer fall in each of a plurality of bins, at least some of the histograms are conditioned on one or more stratification variables, the storage medium is structured for histograms to be accessible by reference to customer, profile variable, and stratification variable, and the accessing step comprises specifying the customer who is party to said new transaction, specifying said at least one obtained new value of a specified profile variable, and specifying said at least one obtained value of a corresponding stratification variable; and f) responsive to (d), using the computer to adjust the relative frequencies stored in at least one histogram, wherein said histogram represents a relative frequency of said specified profile variable for said specified customer, conditioned on said specified value of a stratification variable, wherein: a stratification variable has discriminating power for a given customer if the histogram of at least a given profile variable for the given customer breaks into sufficiently different histograms when it is conditioned on different values of the stratification variable, the difference between the histograms being measured as a value of a statistical function, and the sufficiency of said difference being determined by comparison to a threshold.