Because of CPI index rounding, the smallest possible change in the late-1950s index translated into an approximately 4-percentage-point swing in annualized 1-month inflation, while by the early 1980s the equivalent effect was roughly one-third as large.
Notes on verification
Directly confirmed by the original FEDS Notes source text and independently corroborated by BLS and Kansas City Fed research papers explaining the rounding mechanism and its diminishing effect as the index base grew. [tier=silver indep_score=0.925 clusters=2 claim_tier=notable]
Sources
- Was There a Great Moderation for Inflation Volatility? (seed:economics_and_business)
- https://www.bls.gov/opub/mlr/2006/10/art5full.pdf (corroboration)
- https://www.kansascityfed.org/documents/5269/pdf-rwp99-08.pdf (corroboration)