# Contract (F2-conf-01)

• Question: average effect of a school-assigned programme on student test scores, with design-valid uncertainty; decide at 5% two-sided whether τ≠0.
• Estimand τ: difference in student-weighted mean score, treated vs control schools (OLS coef of score on treated with intercept). Meaningful as a causal effect assuming (as-if) random school-level assignment; inference assumes schools independent, students within school correlated.
• Outputs: out/results.json (task_id, tau_hat, se_iid, se_cluster, p_value, tau_ci_low, tau_ci_high, effect_significant_5pct, icc_hat, n_schools, n_treated_schools, n_analysed, feasibility, feasibility_reason, data_issues, n_input_rows, random_seed), out/report.md (Question; Data and exclusions; Method; Results; Uncertainty; Limitations and open issues), out/analysis.py, out/claims.json (incl. claim on 5% significance).
• Information rule: only data/schools.csv.
• Invalidity: using iid SE for the decision; treatment varying within school; too few clusters for cluster inference (40 here, adequate).