1step,rule,n_before,n_after,n_removed,rationale21_dedup,"keep one row per (iso3, year); duplicates had identical values",439,416,23,country identified by iso3; at most one observation per country-year32_drop_missing,drop country-years with empty life_expectancy,416,415,1,empty cell = no recorded value; no imputation allowed43_balanced,keep countries with a recorded value in every year 2000-2022,415,345,70,balanced-panel estimand: fixed composition across years5