3. A cyclical (C) pattern exists when the data exhibit rises and cyclical falls that are not of a ¯xed period. For economic series, these are usually due to economic °uctuations such as those asso-

ciated with the business cycle. The sales of products such as automobiles, steel, and major appliances exhibit this type of pattern. The clay brick production shown in Figure 1-2d

(p. 7) shows cycles of several years in addition to the quarterly seasonal pattern. The major distinction between a seasonal and a cyclical pattern is that the former is of a constant length and recurs on a regular periodic basis, while the latter varies in length. Moreover, the average length of a cycle is usually longer than that of seasonality and the magnitude of a cycle is usually more variable than that of seasonality.