Decisions 32-33: negative controls

Co-Authored-By: Claude Opus 5.5 <[email protected]>

docs/decisions.md

@@ -57,3 +57,10 @@ Each decision is listed with the date and the reason for it. Settled decisions a
 | 29 | **Replicates:** 100 at draft, 500 at final. MCSE is reported. | MCSE for coverage is about 1% at 500 replicates. |
 | 30 | **Figure 1, the "estimand ladder":** one row per method. Each row shows a hollow dot for the method's own truth, a filled dot with interval for its estimate, and a line for the clinically relevant truth. Panels are worlds; colour is the physician variant. Shown for the null and harm scenarios. **Figure 2:** false-alarm rate by threat and physician variant. | One picture that shows both the question gap and the estimation bias. |
 | 31 | **Next:** the analysis plan (md plus docx), then the table of claudication RCTs, then the build. The docs are committed on the branch `analysis-plan`. | |
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+## Round 6: negative controls (2026-10-27)
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+| # | Decision | Why |
+|---|---|---|
+| 32 | **Three negative controls.** **NCO-1:** hip fracture / pneumonia admission. Shares the latent patient frailty, severity and smoking, so it targets factor 5. **NCO-2:** varicose vein ablation by the same physician. Shares physician procedural style, so it targets factors 2–3. **NCE:** early low-value procedure (e.g. vein ablation) within 6 months, which shares both. All three are generated only from latent traits and never depend on PVI, so their true effect is exactly 0. They go through the same method × physician-variant pipeline as MALE. | Negative controls are the practical bias check available in real claims. CCW and landmark condition on survival, so the controls also need testing under each design. |
+| 33 | **Main text (Figure 3 / Table 3):** how accurately the negative controls detect bias. A control is "flagged" if its CI excludes 0. Bias in the MALE risk difference counts if |bias| > 1 percentage point. Report sensitivity and specificity, plus how much bias can sit behind a clean negative control. **Supplement:** each control's own false-positive rate. | Answers a new, practical question: what does a clean negative control actually tell a surgeon? |