1[2 {"id":"C1","text":"Over 1960Q1-2019Q4 the full-sample OLS Okun coefficient is about -0.26 pp per 1% quarterly real GDP growth, with intercept about 0.18 pp.","results_keys":["effect_estimate","intercept","n_analysed","sample_start","sample_end"],"status":"supported","caveat":"Reduced-form association, not causal; 2026 data vintage."},3 {"id":"C2","text":"The HAC (Newey-West, 4 lags) 95% CI for beta, [-0.326, -0.186], lies entirely below zero, so conclusion = negative_effect.","results_keys":["effect_se","hac_lags","effect_ci_low","effect_ci_high","conclusion"],"status":"supported","caveat":"Normal approximation; conclusion robust to lags 0-12 (hac_se_by_lag)."},4 {"id":"C3","text":"Output growth explains a substantial share of quarterly unemployment changes: residual RMSE 0.250 pp vs 0.325 pp for the mean-only baseline (R2 about 0.41).","results_keys":["model_metric","baseline_metric","r_squared"],"status":"supported","caveat":"In-sample fit only; no out-of-sample evaluation."},5 {"id":"C4","text":"Subperiod slopes are nearly identical (-0.259 for 1960-1983, -0.273 for 1984-2019); the HAC test of the slope difference alone does not reject.","results_keys":["beta_sub1","beta_sub2","hac_wald_slope_diff_p","beta_sub1_hac_se","beta_sub2_hac_se"],"status":"supported","caveat":"Imposed break date."},6 {"id":"C5","text":"The classical Chow test rejects joint equality of (alpha, beta) across the 1984Q1 split (F = 6.09, p = 0.0026), so stability_conclusion = unstable; a HAC Wald joint test also rejects.","results_keys":["chow_f_stat","chow_p_value","stability_conclusion","chow_df","hac_wald_joint_p"],"status":"supported","caveat":"Classical Chow assumes homoskedastic, serially uncorrelated, equal-variance errors, likely violated; break date imposed; instability concerns the (alpha,beta) pair, not the slope."},7 {"id":"C6","text":"The growth rate consistent with stable unemployment (-alpha/beta) fell from about 0.98% to about 0.55% per quarter between subperiods.","results_keys":["okun_growth_sub1","okun_growth_sub2","intercept_sub1","intercept_sub2"],"status":"supported","caveat":"Point estimates only; the HAC test of the intercept difference alone is not significant (hac_wald_intercept_diff_p = 0.25)."}8]9