“…In general, the firm may find it advantageous to compute in subsequent periods (say, tm, m = 1,2,...) deviations from the mean values of random variables η i,t-m coming from different subsets of sources (say, S t-m , m = 1,2,...) and use them for the estimation of the total deviation from the expected demand in period t (rational strategy requires that sources of demand should be analyzed cyclically one after the other) (see Cukrowski, 1996).…”