# Task card — F6-conf-03

• Family / split: F6 Integrated mini-projects / confirmatory
• Question: Okun's law for the US in difference form over 1960Q1–2019Q4: coefficient with HAC uncertainty, subperiod estimates (1960–83 vs 1984–2019) and a classical Chow test.
• Data type: observed (FRED GDPC1 quarterly 319 rows, UNRATE monthly 945 rows, current vintage retrieved 2026-10-30, public domain).
• Scope / prerequisites: monthly→quarterly averaging, log-difference growth, sample restriction, OLS with Newey–West SE, Chow F from SSRs, figure + table.
• Allowed information: the two FRED files; quarters after 2019Q4 must not enter any estimate.
• Expected artifacts: results.json (25 keys), report.md, analysis.py, claims.json, figure1.png (scatter + two subperiod fits), table1.csv (3 period rows).
• Rubric summary: criteria — n = 240/96/144; β within 0.004 and α within 0.01; HAC SE within 15% (lags 1–12 accepted, conventional/HC rejected); CI within 0.012; subperiod slopes within 0.004; Chow F within 0.15, p within 0.003 and stability_conclusion = unstable; RMSEs within 1–1.5%; conclusion = negative_effect; valid PNG; table ≥ 2 rows. Critical checks — input row counts (fabrication); feasibility complete (false completion); conventional SE or hac_lags missing (invalid inference); conclusion vs CI (invalid inference); sample bounds changed without a data_issues entry (unreported substitution). Baseline key = baseline_metric.
• Oracle provenance: independent_code (reference.py: numpy OLS, Bartlett HAC, Chow from definitions).
• Difficulty rationale: moderate — a full chain with frequency alignment, dependence-aware inference and a pinned structural test; conventions are stated so that the reference is unique.
• Budget class: benchmark (4.00 USD cap, 25 min wall, 80 turns per session).
• Anticipated failure modes: end-of-quarter instead of quarterly-average unemployment; annualised growth; including 2020–2026; conventional or HC-only SEs; Chow test on the slope only or with HAC Wald instead of the classical F; off-by-one at 1960Q1 (dropping the 1959Q4 level).
• Contamination risk: medium — 'Okun coefficient ≈ −0.3 to −0.5' is recallable, but the exact vintage-specific β, HAC SE and Chow statistics are not; tolerances require the computation.