1[2 {"id":"C1","text":"Over 1960Q1-2019Q4 the Okun coefficient is about -0.26 pp per 1% q/q real GDP growth, and its HAC 95% CI lies entirely below zero.","results_keys":["effect_estimate","effect_se","effect_ci_low","effect_ci_high","hac_lags","conclusion","n_analysed"],"status":"supported","caveat":"Reduced-form association, not causal; HAC lag chosen by rule of thumb only."},3 {"id":"C2","text":"The OLS model improves on the mean-only baseline (residual RMSE 0.250 vs 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%, so the relation is classified unstable.","results_keys":["chow_f_stat","chow_p_value","stability_conclusion","n_sub1","n_sub2"],"status":"supported","caveat":"Classical Chow test assumes homoskedastic, uncorrelated errors; break date imposed."},5 {"id":"C4","text":"The instability comes from the intercept: subperiod slopes are nearly identical and a HAC test finds no slope break, while the HAC joint test still rejects.","results_keys":["beta_sub1","beta_sub2","intercept_sub1","intercept_sub2","hac_wald_break_slope_p","hac_wald_break_joint_p"],"status":"supported","caveat":"Supplementary diagnostic beyond the required outputs; single lag choice."},6 {"id":"C5","text":"HAC standard errors are substantially larger than iid OLS standard errors.","results_keys":["effect_se","ols_se_beta_iid"],"status":"supported","caveat":"Ratio depends on lag length."}7]8