1[2 {"id":"C1","text":"Over 1960Q1-2019Q4 the Okun coefficient is about -0.26 pp per 1% quarterly real growth, with HAC 95% CI entirely below zero.","results_keys":["effect_estimate","effect_se","hac_lags","effect_ci_low","effect_ci_high","conclusion"],"status":"supported","caveat":"Reduced-form association, not causal; current-vintage data."},3 {"id":"C2","text":"The regression on growth reduces RMSE of quarterly unemployment changes from 0.325 pp (mean-only baseline) to 0.250 pp.","results_keys":["baseline_metric","model_metric"],"status":"supported","caveat":"In-sample fit only; no out-of-sample evaluation."},4 {"id":"C3","text":"The classical Chow test rejects joint equality of (alpha, beta) between 1960-1983 and 1984-2019 at 5%.","results_keys":["chow_f_stat","chow_p_value","stability_conclusion"],"status":"supported","caveat":"Classical Chow test assumes iid errors, which fail here; a HAC Wald test (diagnostics.json) agrees."},5 {"id":"C4","text":"The subperiod slopes are nearly identical (-0.259 vs -0.273); the instability is driven by the intercept rather than the Okun slope.","results_keys":["beta_sub1","beta_sub2","intercept"],"status":"supported","caveat":"Slope-only HAC Wald test (p=0.85) and subperiod intercepts are in out/diagnostics.json and out/table1.csv, not in results.json; break date imposed a priori."}6]7