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Once the stage, flow or damage data have been computed for the base and decade years by interpolation then expected annual damage is computed for the base, decade, and input data years. For the remaining years expected annual damage is computed by linear interpolation using expected annual damage previously computed for the base, decade, and input data years. 14. AFFLUENCE FACTOR An increase or decrease in the contents value of residential struc- tures during a period of analysis can be taken into account in the computation of expected annual damage by inputting the affluence factor as a ratio (1.04 indicates a 4 percent affluence factor), the damage category (residential contents), and the input data years to which it applies (RV card). This factor can be applied to each plan with a damage category for residential contents. It is required that the maximum (75 percent) level for the value of contents as a percentage of the value of structure be determined outside the program in establishing the last year the factor applies. The effect of affluence is displayed in the equivalent annual damage for the residential contents category and in the total damages for each year. This manner of handling affluence is an interim procedure until a more complete algorithm can be written for the computer program. 15. EQUIVALENT ANNUAL FLOOD DAMAGE Up to three discount rates may be used to compute equivalent annual flood damage (J2 card). Prior to discounting, expected annual flood damage is computed for each year of the period of analysis. Each year's expected annual damage which is assumed to occur at the end of the year is discounted back to the beginning of the base year, then amortized over the period of analysis. The discounting formula used is P = t 1 (1 + i)N (Single payment present- worth factor) where: P = Present amount (at beginning of base year) of some future amount F = Future amount N = Number of years the future amount is from present i = Di scount rate 10 Il