# Contract — F1-conf-02
**Question:** change in life expectancy at birth 2000→2022 across a fixed (balanced) set of countries.
**Estimands:** for each year, unweighted mean of life expectancy over countries (iso3) with a recorded value in every year 2000–2022, each counted once; main: mean 2000, mean 2022, difference; composition of the balanced set. Meaningful assuming WDI values comparable across years and one obs per country-year. Unweighted country mean (not population-weighted).
**Baseline:** mean of 2022 over all distinct countries with a recorded 2022 value (descriptive only).
**Outputs:** out/results.json (task_id, n_countries_total, n_countries_balanced, n_countries_incomplete, balanced_countries, n_analysed, mean_2000_balanced, mean_2022_balanced, change_2000_2022_balanced, mean_2022_all_available, feasibility, feasibility_reason, data_issues, n_input_rows, random_seed), out/analytic.csv, out/exclusions.csv, out/report.md, out/analysis.py, out/claims.json.
**Info rules:** only the CSV; no imputation/interpolation/lookup; empty cell = missing; country = iso3; ≤1 obs per country-year.
**Invalid if:** duplicates counted twice; conflicting duplicate values (would be unresolvable without external info); missing values imputed; no country complete (infeasible).