# Index Choice and Chained CPI There is no single true inflation rate. There is a family of indexes, each making different assumptions, and the differences compound. Because vast portions of the federal government are indexed — tax brackets, [[Social Security]] benefits, poverty thresholds, benefit eligibility — **choosing among them redistributes hundreds of billions of dollars without anyone voting on a benefit cut or a tax increase.** ## The index family **CPI-U** — urban consumers, the headline [[Consumer Price Index]]. **CPI-W** — urban wage earners and clerical workers. A narrower population. This is the index used for Social Security cost-of-living adjustments. **C-CPI-U (chained CPI)** — allows the basket of goods to change as consumers substitute between products in response to relative price changes. **PCE price index** — the Bureau of Economic Analysis measure, broader in scope; the Federal Reserve's preferred gauge for its target. **CPI-E** — an experimental index for households aged 62 and over, weighting medical care and housing more heavily. ## What chaining does Standard CPI holds a fixed basket and asks what it costs. If beef prices spike and shoppers switch to chicken, fixed-basket CPI still prices the beef. Chained CPI updates the basket to reflect the substitution. The economic rationale is real: consumers do substitute, and a fixed basket overstates the cost of maintaining a given standard of living. This is called substitution bias, and it is a genuine measurement problem. Chained CPI runs roughly **0.25 percentage points lower per year** than standard CPI. That sounds like a rounding error. Over a retirement, it is not — compounding at a quarter point annually produces a benefit several percentage points lower after a decade and substantially lower after twenty-five years. **The cut is invisible in any single year and large in the aggregate, which is precisely what makes it politically attractive.** ## The contested premise The substitution logic assumes the switch is voluntary and welfare-neutral — that trading beef for chicken leaves you equally well off. For discretionary consumption that is often reasonable. For a household already at the margin, "substitution" may mean a worse diet, a delayed prescription, or a colder apartment. Treating a forced downgrade as a neutral preference shift is an assumption about welfare, not a measurement. The counter-index makes the point sharply: **CPI-E, built for older households, generally runs *higher* than CPI-W**, because seniors spend disproportionately on medical care and housing, the fastest-rising categories. If the goal were to measure the inflation experienced by beneficiaries, CPI-E is the better instrument and it points the other way. So there are two available technical corrections. One reduces benefits and one increases them. **Only one of them has ever been seriously advanced in budget negotiations**, and that asymmetry is the political content the technical framing conceals. ## Where it was actually adopted Chained CPI was repeatedly proposed for Social Security COLAs across multiple administrations and never enacted — it is politically radioactive when described as what it is. It *was* enacted for the tax code. The [[Tax Cuts and Jobs Act]] (2017) switched indexation of tax brackets, the standard deduction, and other parameters from CPI-U to chained CPI. Because brackets now rise more slowly than actual price growth, taxpayers drift into higher brackets over time — bracket creep, reintroduced by index selection. The structural detail worth noting: **the individual rate cuts in that law were scheduled to expire; the chained-CPI switch was permanent.** The provision that reduced taxes was temporary and the provision that raises them over time was not. That is a [[CBO Baselines and Scoring Windows]] artifact, and it produced a durable revenue increase that no one had to cast a vote for. ## The general lesson Indexation converts a measurement decision into a fiscal decision. Whenever a large program's payouts depend on an index, **the index becomes a policy instrument, and changing it is a way to legislate without appearing to legislate.** The technical framing is not incidental — it is what allows the change to pass. See [[The Politics of Official Statistics]] for what happens when the agencies producing these indexes come under direct political pressure. ## Related [[Rate Versus Level]] · [[CBO Baselines and Scoring Windows]] · [[GDP as a Constructed Measure]] · [[The Politics of Official Statistics]] · [[Consumer Price Index]] · [[Inflation]] · [[Social Security]] · [[Tax Cuts and Jobs Act]] · [[Mathematics and Power Hub]]