1[2 {"id":"C1","text":"Over 1960Q1-2019Q4 the OLS Okun coefficient is about -0.256 pp per 1% quarterly real GDP growth, with a HAC (NW, 4 lags) 95% CI of about [-0.326, -0.186], so the effect is negative.","results_keys":["effect_estimate","effect_se","hac_lags","effect_ci_low","effect_ci_high","conclusion"],"status":"supported","caveat":"Reduced-form association on revised (current-vintage) data; normal-approximation CI."},3 {"id":"C2","text":"Growth explains a substantial part of quarterly unemployment changes: residual RMSE 0.250 pp vs 0.325 pp for the mean-only baseline.","results_keys":["model_metric","baseline_metric","r_squared"],"status":"supported","caveat":"In-sample fit only."},4 {"id":"C3","text":"The classical Chow test rejects joint equality of (alpha, beta) between 1960Q1-1983Q4 and 1984Q1-2019Q4 at 5% (F=6.09, p=0.0026), so the relation is classified unstable.","results_keys":["chow_f_stat","chow_p_value","stability_conclusion","hac_wald_break_p"],"status":"supported","caveat":"Classical test assumes equal variances (residual variance ratio ~1.63); a HAC Wald test gives the same verdict."},5 {"id":"C4","text":"The subperiod slopes are nearly identical (-0.259 vs -0.273); the slope difference is not individually significant, and the instability appears to come mainly from the intercept.","results_keys":["beta_sub1","beta_sub2","intercept_sub1","intercept_sub2","hac_p_slope_diff","hac_p_intercept_diff"],"status":"supported","caveat":"The intercept shift is also not individually significant (p=0.25); only the joint test rejects. The attribution to the intercept rests on point estimates."},6 {"id":"C5","text":"The sign conclusion is robust to the HAC lag length (0 to 12 lags).","results_keys":["hac_se_by_lag"],"status":"supported","caveat":"Only Bartlett kernel lags 0,2,4,8,12 were checked."}7]8