# Contract — F1-conf-01
**Question.** 12-month growth of CPIAUCSL (SA) for each month 2001-01..2026-09, g_t = 100(P_t/P_{t-12} - 1), with P_t taken from the most recent vintage covering month t (2026-10-28 vintage for 2014-01..2026-09, 2016-07-15 vintage otherwise). Lags for 2001-01..2014-12 therefore come from 2000-01..2013-12 in the 2016 vintage.
**Estimands.** g_t per month; mean over window; sub-period means 2001-01..2013-12 and 2014-01..2026-09; g at 2014-06, 2016-07, 2020-05, 2022-06, 2026-09; max/min and months. Meaningful under: the vintage-splice rule (mixing vintages across a ratio at the 2014 boundary is accepted by the rule), no imputation.
**Outputs.** out/results.json (keys listed in TASK.md), out/analytic.csv (date,cpi,cpi_lag12,vintage_used,growth_12m; n_analysed rows), out/exclusions.csv, out/report.md (6 sections), out/analysis.py, out/claims.json.
**Information rules.** Most-recent-vintage per month; no interpolation/imputation; missing g_t counted; only data/ files.
**Invalidity.** Using assembled file values where they conflict with vintage files; imputing missing months; using older vintage where newer covers the month.