# Contract — F1-conf-02

Question: How much did life expectancy at birth (WDI SP.DYN.LE00.IN) change from 2000 to 2022 across a fixed set of countries? Estimands: balanced-panel means — for 2000 and 2022, the unweighted mean of life expectancy over countries (iso3) with a recorded non-missing value in every year 2000–2022, each counted once; their difference; the composition of the balanced set. Meaningful as a description of this fixed country set (not population-weighted, not a sample of a wider population). Baseline: naive mean of all distinct countries with a 2022 value. 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 (6 sections), out/analysis.py, out/claims.json. Information rules: only the CSV; no imputation/interpolation/lookup; country = iso3; ≤1 obs per country-year. Invalidity: conflicting duplicate values for an (iso3, year) with no rule to choose; empty balanced set; double-counting a country.