A standard succession of values of demand-over-time data used in forecasting seasonal items. This series of factors is usually based on the relative level of demand during the corresponding period of previous years. The average value of the base series over a seasonal cycle will be 1.0. A figure higher than 1.0 indicates that the demand for that period is more than the average; a figure less than 1.0 indicates less than the average. For forecasting purposes, the base series is superimposed upon the average demand and trend in demand for the item in question. Synonym: Base Index. Also see: Seasonality.