Original sentence: Especially since 1980, the definition of CPI has been altered repeatedly, though economists disagree whether the index underestimates or overestimates the true rate of decline in purchasing power.The CPI has powerful political ramifications, and administrations of both parties have been tempted to change the basis for its calculation
Edited sentence: Especially since 1980, the definition of CPI has been altered repeatedly, progressively underestimating the true rate of decline in purchasing power.The CPI has powerful political ramifications, and Administrations of both parties have been tempted to change the basis for its calculation