Make reasonable adjustments based on monthly carryover.

A quarterly or monthly time series is often affected by intra-year seasonal changes caused by seasonal factors such as climatic conditions, production cycles, holidays, and sales.

Because the impact of these factors is sometimes large enough to obscure the short-term basic trend of time series changes, seasonal adjustments must be made if we want to grasp the quarterly or monthly changes in economic operations. By subtracting the average change over the past few years from the change, you can tell whether the rise or fall is unusual or simply seasonal.