1# Contract — F2-conf-042**Question.** Okun's law in U.S. quarterly data: slope β of the linear projection Δu_t = α + β g_t + e_t, with uncertainty robust to serial correlation.3**Estimands.** β (pp change in quarterly-average unemployment rate per 1% q/q real GDP growth, non-annualised), α, R². u_t = mean of 3 monthly UNRATE values in quarter t; Δu_t = u_t − u_{t−1}; g_t = 100·ln(GDPC1_t/GDPC1_{t−1}). β is a linear-projection coefficient (meaningful under covariance stationarity of (Δu, g)); HAC SE valid under weak dependence + finite fourth moments.4**Sample.** 240 quarters 1960Q1–2019Q4; 1959Q4 levels used only for first differences. Do not extend the window.5**Outputs.** out/results.json (task_id, beta_hat, alpha_hat, r_squared, se_iid, se_hac, hac_lags, beta_ci_low, beta_ci_high, okun_negative_5pct, mean_growth, first_quarter, last_quarter, 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; out/figure1.png (scatter + fitted line).6**Information rules.** Only data/ files, current vintage taken as given; no extension of window.7**Invalidity conditions.** Missing months/quarters in window (incomplete quarterly averages), duplicates, non-numeric values; n ≠ 240; using annualised growth; using data outside window beyond 1959Q4 levels.8