1step,rule,n_before,n_after,n_removed,rationale21,"Remove duplicate (iso3, year) rows",439,416,23,Each country contributes at most one observation per year; duplicates had identical values.32,Remove country-years with no recorded life_expectancy,416,415,1,Empty cell = no recorded value; no imputation allowed.43,"Keep only countries with a recorded value in every year 2000-2022 (drops BGD, CHE, ETH, IND, NGA)",415,345,70,Balanced-panel estimand: fixed country set across all years.5