1. A processor-based method comprising: determining an unconditional probability density function (PDF) for a ratio of a cumulative attribute's current value to an associated future value for the cumulative attribute; determining an unconditional PDF for a future value of the cumulative attribute; combining the unconditional PDFs with a current value of the cumulative attribute to obtain a function indicative of a conditional PDF for the future value; operating on the function to obtain at least one forecast; and communicating the forecast to a user.