To estimate possible bias in the measurement of CPI, Lisa Martin calculated headline inflation from underlying 8-digit categories using the 2016 CPI weights and 2023 CPI weights. Codera estimates that CPI has been lower by an average of 0.5 percentage points since 2009 if measured using the most recent CPI weights.
The most recent CPI weights were measured in 2023 but only applied in CPI measurement from 2025 onwards. A lower CPI estimate from updated weights suggests that inflation may be overstated at specific points of time when using outdated spending patterns, and newer weights provide a more accurate reflection of actual price changes experienced by consumers. As the second chart shows, inflation has tended to be higher in real-time than subsequently measured when weights are re-estimated.
