Reconsideration of Weighting and Updating Procedures in the US CPI

Summary In 2002, the US Bureau of Labor Statistics (BLS) introduced a supplemental C-CPI-U employing a superlative formula to provide a closer approximation to a cost-of-living index (COLI). This paper focuses on whether the BLS can improve upon the headline CPI-U’s current biennial weight update process, thereby reducing the CPI-U’s growth rate and bringing the index closer to the C-CPI-U. We begin by estimating superlative price indexes for 1999 through 2007 along with indexes based on the constant-elasticity-of-substitution demand model. Our analyses confirm that the consumer expenditure data underlying the CPI imply substantial consumer substitution, implying that the CPI-U’s Lowe index formula yields higher inflation estimates than would a true COLI. Simulating feasible weight update processes, we find that a Lowe index with two-year weight reference periods but annual updating rises by about 0.03 percentage points less per year than the CPI-U. Another 0.01 percentage point on average is subtracted by imposing annual revision with one-year base periods. Thus, indexes with more timely weights may offer improved representation of current price change, as well as closer approximations to a COLI.