1. A computer-implemented method performed by a computer processor, comprising: (a) receiving by the computer processor a training set of elements, each element in the training set being assigned to one of a plurality of categories and having one of a plurality of content profiles associated therewith; (b) receiving by the computer processor a population set of elements, each element in the population set having one of the plurality of content profiles associated therewith; and (c) calculating by the computer processor applying the stacked regression method, based on the content profiles associated with and the categories assigned to elements in the training set and the content profiles associated with the elements of the population set, a distribution of elements of the population set over the categories.