1. A processor-based method comprising: determining, by a processor, 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, by the processor, an unconditional PDF for a future value of the cumulative attribute; combining, by the processor, 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, by the processor, on the function to obtain at least one forecast; and communicating the forecast to a user, wherein said combining comprises: finding a set of ratios by dividing the current value of the cumulative attribute by each of a set of potential future values; for each potential future value in said set of potential future values, evaluating the unconditional ratio PDF at the ratio associated with the potential future value; evaluating the unconditional future value PDF at the potential future value; multiplying the evaluated unconditional PDFs to determine a product; and dividing the product of the evaluated unconditional PDFs by the potential future value.