# Contract — F1-conf-02

Question. How did life expectancy at birth (WDI SP.DYN.LE00.IN, years) change from 2000 to 2022 across a fixed set of countries? Estimands. Balanced-panel means: for each year, the unweighted mean over countries (iso3) with a non-missing value in every year 2000–2022, each country counted once. Main: mean_2000_balanced, mean_2022_balanced, their difference; composition of the balanced set. Descriptive baseline: mean over all distinct countries with a recorded 2022 value (each once). Meaningful as a descriptive, unweighted country average (not population-weighted); no sampling-based inference implied. 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 (iso3,country_name,year,life_expectancy; n_analysed rows, unique iso3-year); out/exclusions.csv (chained ledger); out/report.md (6 sections); out/analysis.py; out/claims.json. Information rules. Only data/life_expectancy_panel.csv. No imputation/interpolation/lookup. Country = iso3; at most one obs per country-year. Invalidity risks. Duplicate country-years counted twice (assembly errors); treating empty cells as values; imputing; country identified by name instead of iso3; conflicting duplicate values (would require a documented decision or make result partial).