# Contract — F1-conf-02

Question: How did life expectancy at birth (WDI SP.DYN.LE00.IN) change from 2000 to 2022 across a fixed set of countries? Estimands: For each year, the unweighted mean of life expectancy over the countries (identified by iso3) that have a recorded value in every year 2000–2022, each counted once. Main quantities: balanced mean 2000, balanced mean 2022, their difference, and the balanced set's composition. Descriptive baseline: unweighted 2022 mean over all distinct countries with a recorded 2022 value. Meaningful as descriptive means of a fixed set of countries. They are not population-weighted, and they are not representative of any wider population. 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. Information rules: use only the CSV. Do not impute, interpolate or look up values. Empty cell = missing. A country is identified by iso3, with at most one observation per year. Invalidity: double-counting duplicate country-years; imputing gaps; conflicting duplicates that cannot be resolved; an empty balanced set.