# Contract — F6-dev-01
**Question.** Does the cross-country Preston curve (LE rising with ln income) hold in the latest usable WDI year, and how strong is it?
**Estimand.** β in the linear projection LE_i = α + β ln(GDPpc_i) + ε_i over countries/economies (equal weights) in the analysis year; GDPpc = PPP constant 2021 intl $. Descriptive/associational only; meaningful as a best linear predictor (no exogeneity needed), inference via heteroskedasticity-robust SE (HC3 chosen).
**Outputs.** out/results.json (analysis_year, n_excluded_missing, baseline_metric, model_metric, pearson_r, r_squared, effect_estimate, intercept, effect_se, effect_ci_low, effect_ci_high, conclusion, task_id, feasibility, feasibility_reason, data_issues, n_input_rows, n_analysed, random_seed), out/figure1.png, out/table1.csv (income_level, n_countries, mean_log_gdp_pc, mean_life_expectancy), out/report.md (6 sections), out/analysis.py, out/claims.json; plus state files and out/exclusions.csv.
**Information rules.** Exclude region == "Aggregates"; analysis year = latest 2015–2023 year with both indicators for >=150 countries; drop missing in that year (count = n_excluded_missing); no imputation; natural log; only the listed files.
**Invalidity/impossibility.** No year with >=150 complete countries; non-positive GDP (log undefined); entity metadata not matching indicator codes; zero variance. If so → premise_invalid / infeasible with nulls.