1[2 {"id":"C1","text":"Over 1960Q1-2019Q4, a 1 pp higher quarterly real GDP growth is associated with a fall of about 0.26 pp in the unemployment rate; the 95% HAC (Newey-West, 4 lags) interval [-0.326, -0.185] lies below zero.","results_keys":["effect_estimate","effect_se","hac_lags","effect_ci_low","effect_ci_high","conclusion"],"status":"supported","caveat":"Contemporaneous association from a static bivariate regression, not a causal effect; revised data vintage."},3 {"id":"C2","text":"Output growth explains a substantial part of unemployment changes: residual RMSE 0.250 pp vs 0.325 pp for the mean-only baseline.","results_keys":["model_metric","baseline_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) across 1960Q1-1983Q4 and 1984Q1-2019Q4 at the 5% level (F = 6.09, p = 0.0026).","results_keys":["chow_f_stat","chow_p_value","stability_conclusion","n_sub1","n_sub2"],"status":"supported","caveat":"Classical Chow assumes iid homoskedastic errors, which the residuals violate (autocorrelation, lower post-1984 variance); a HAC Wald analogue also rejects (p = 0.005, supplementary)."},5 {"id":"C4","text":"The Okun slope itself is nearly identical in the two subperiods (-0.259 vs -0.273); the instability mainly reflects a lower intercept / break-even growth rate after 1984.","results_keys":["beta_sub1","beta_sub2","intercept"],"status":"supported","caveat":"Point estimates support it and the HAC slope-only difference test does not reject (p = 0.85, supplementary), but the intercept-only test is also individually insignificant (p = 0.26); suggestive, not established."}6]7