# Contract — F6-conf-03 (Okun's law, US 1960Q1–2019Q4)

**Question.** How strongly does the quarterly change in the US unemployment rate respond to quarterly real GDP growth, and is that response stable across 1960–1983 vs 1984–2019?

**Estimands.** β (and α) in Δu_t = α + β g_t + ε_t, OLS, 1960Q1–2019Q4 (n = 240). u_t = mean of the 3 monthly UNRATE values in quarter t; Δu_t = u_t − u_{t−1}; g_t = 100·Δln GDPC1_t (not annualised). β is a reduced-form conditional association (an "Okun coefficient"), meaningful as a descriptive/predictive slope under linearity and approximate stationarity of the relationship within each sample; it is not a structural causal effect. Inference: Newey–West (Bartlett) HAC SE for full-sample β, lag reported; 95% CI from that SE. Stability: subperiod OLS slopes (1960Q1–1983Q4, n=96; 1984Q1–2019Q4, n=144) and classical Chow SSR F-test, df (2, n−4), 5% level.

**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 (scatter + two subperiod lines); out/table1.csv (period,n,intercept,slope,slope_se; 3 rows); out/report.md (6 sections in order); out/analysis.py; out/claims.json.

**Information rules.** Only data/GDPC1.csv and data/UNRATE.csv. No quarter after 2019Q4 may enter any estimate (1959Q4 levels used only to form the 1960Q1 differences). Data vintage is the 2026 FRED vintage (as given).

**Invalidating conditions.** Missing monthly UNRATE or GDPC1 values inside 1959Q4–2019Q4; incomplete quarters; using post-2019 data; non-HAC SE for full-sample β; wrong Chow df.