1[2 {"id":"C1","text":"The full-sample Okun coefficient is about -0.26 pp per 1% quarterly real GDP growth, and its 95% HAC confidence interval lies below zero (negative_effect).","results_keys":["effect_estimate","effect_se","effect_ci_low","effect_ci_high","hac_lags","conclusion"],"status":"supported","caveat":"Reduced-form contemporaneous association; HAC lag chosen by rule of thumb, but the SE is insensitive across lags 0-12."},3 {"id":"C2","text":"Output growth explains a substantial share of the variance of the change in unemployment: residual RMSE 0.250 pp vs a mean-only baseline of 0.325 pp.","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) across 1960Q1-1983Q4 and 1984Q1-2019Q4 at 5% (unstable).","results_keys":["chow_f_stat","chow_p_value","stability_conclusion"],"status":"supported","caveat":"The classical test assumes equal error variances, which are rejected (variance-ratio p≈0.009); a HAC Wald test gives the same conclusion."},5 {"id":"C4","text":"The instability comes from the intercept; the subperiod slopes are almost identical and their equality is not rejected.","results_keys":["beta_sub1","beta_sub2","intercept_sub1","intercept_sub2","supp_hac_wald_slope_p","supp_hac_wald_joint_p"],"status":"supported","caveat":"Supplementary test, not required by the task; the break date is imposed."}6]7