1# Contract — F2-conf-042**Question.** Okun's law in U.S. quarterly data: how does the quarterly change in the unemployment rate co-move with quarterly real GDP growth, with inference robust to serial correlation?34**Estimand.** β in the linear projection Δu_t = α + β g_t + e_t, u_t = quarterly mean of 3 monthly UNRATE values (pp), Δu_t = u_t − u_{t−1}, g_t = 100·ln(GDPC1_t/GDPC1_{t−1}) (percent, not annualised). Sample 1960Q1–2019Q4 (240 quarters; 1959Q4 levels used for first differences). β is a linear-projection coefficient (descriptive, not causal); it is meaningful under covariance stationarity of (Δu, g) over the sample. HAC SE valid under weak dependence / mixing, with bandwidth growing slowly.56**Outputs.** out/results.json keys: 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. Also out/report.md (Question; Data and exclusions; Method; Results; Uncertainty; Limitations and open issues), out/analysis.py, out/claims.json, out/figure1.png.78**Information rules.** Only data/ files; current vintage, treated as given. Observations outside 1960Q1–2019Q4 used only for 1959Q4 levels; window not extended.910**Invalidity/impossibility.** Missing monthly values or GDP inside 1959Q4–2019Q4 (incomplete quarters), wrong sample size (≠240), annualised growth, using data outside window in regression.11