1[2 {"id":"C1","text":"Full-sample Okun coefficient is about -0.26 pp per 1% quarterly real GDP growth, with a 95% HAC interval entirely below zero (negative_effect).","results_keys":["effect_estimate","effect_se","effect_ci_low","effect_ci_high","hac_lags","conclusion"],"status":"supported","caveat":"Reduced-form association; contemporaneous-only specification; revised GDP vintage."},3 {"id":"C2","text":"The regression reduces RMSE from 0.325 pp (mean-only baseline) to 0.250 pp.","results_keys":["baseline_metric","model_metric","r_squared_full"],"status":"supported","caveat":"In-sample fit only."},4 {"id":"C3","text":"The classical Chow test rejects joint equality of (alpha, beta) across 1960-83 and 1984-2019 at 5% (unstable).","results_keys":["chow_f_stat","chow_p_value","stability_conclusion"],"status":"supported","caveat":"Classical test assumes i.i.d. errors; serial correlation likely makes it over-reject; break date imposed."},5 {"id":"C4","text":"The subperiod slopes are nearly equal (-0.259 vs -0.273); the instability is driven by an intercept decline (0.254 to 0.152), and a HAC slope-only break test does not reject (p=0.85).","results_keys":["beta_sub1","beta_sub2","intercept_sub1","intercept_sub2","slope_break_hac_pvalue"],"status":"supported","caveat":"Supplementary diagnostic, not part of the required test; interpretation of the intercept shift as lower trend growth not formally tested."},6 {"id":"C5","text":"The sign conclusion is robust to the HAC lag length (0, 2, 4, 8, 12 lags).","results_keys":["hac_se_sensitivity","effect_estimate"],"status":"supported","caveat":"Only Bartlett kernel examined."}7]8