2. A seasonal (S) pattern exists when a series is in°uenced by seasonal seasonal factors (e.g., the quarter of the year, the month, or day of the week). Sales of products such as soft drinks, ice creams, and household electricity consumption all exhibit this type of pattern. The beer data show seasonality with a peak in production in November and December (in preparation for Christmas) each year. Seasonal series are sometimes also called

\periodic" although they do not exactly repeat themselves over periodic each period.