The Taiwan Business Cycle Indicators compiled by the National Development Council are in reference to the method adopted by the OECD, without the concept of base period. However, the composite index, is passed through amplitude adjustment and long-term trend restored of the trend-adjusted index, and the long-term trend is derived from estimates of the industrial production index. Since the industrial production index replaces base period about every five years, the long-term trend estimates will change, thus leading to the sharp correction of the composite index.