# Contract — F6-conf-03 (Okun's law, US 1960–2019)

Question: how strongly does the quarterly change in the US unemployment rate respond to quarterly real GDP growth, and is the response stable across 1960Q1–1983Q4 vs 1984Q1–2019Q4? Estimand: β in Δu_t = α + β g_t + ε_t, Δu_t = change in quarterly-average UNRATE (pp), g_t = 100·Δln GDPC1 (% q/q, not annualised), t = 1960Q1..2019Q4 (240 obs; 1960Q1 uses 1959Q4 levels). β is a reduced-form statistical association (conditional mean slope), meaningful as such under linearity and stable parameters within the sample; not a causal effect. Uncertainty: Newey–West (Bartlett) HAC SE for full-sample β, lag reported; 95% CI = β ± 1.96·SE (normal). Stability: separate OLS by subperiod; classical Chow SSR F-test, df (2, n−4). Outputs: out/results.json (keys: sample_start, sample_end, n_sub1, n_sub2, baseline_metric, model_metric, effect_estimate, intercept, effect_se, hac_lags, effect_ci_low, effect_ci_high, beta_sub1, beta_sub2, chow_f_stat, chow_p_value, stability_conclusion, conclusion, task_id, feasibility, feasibility_reason, data_issues, n_input_rows, n_analysed, random_seed); out/figure1.png; out/table1.csv (period,n,intercept,slope,slope_se; 3 rows); out/report.md (6 sections); out/analysis.py; out/claims.json. Information rules: quarterly u = mean of 3 months; no quarter after 2019Q4 in any estimate; only the given files. Invalidity / impossibility: missing data inside 1959Q4–2019Q4, incomplete quarters, or file hash mismatch would compromise; using post-2019 data would violate rules.