If the market clustering were purely an artifact of case-finding that sought market connections, then cases lacking any market link (found by other routes) should not centre on the market; instead they centre on it even more tightly. The authors add that the spatial relationship persists after removing the two-thirds of unlinked cases residing nearest the market. This makes market-link ascertainment an implausible sole explanation for the clustering. Validity caveat (for scoring): critics (Stoyan-Chiu; Weissman’s proximity-ascertainment-bias argument) contend the residential locations themselves are ascertainment-biased - early case-finding concentrated on central-Wuhan hospitals near the market - so a residual location bias could still inflate the signal even among unlinked cases.
Validity verdict
status: approved; reason_if_not_false: checked. Premise: unlinked December cases lived even closer to the market than market-linked cases. Load-bearing step: if the clustering were purely an artifact of case-finding that sought market connections, cases lacking any market link (found by other routes) should not center on the market; they center on it even more tightly (and the relationship persists after dropping the two-thirds of unlinked cases nearest the market), so market-link ascertainment is an implausible sole explanation. Traced directly — this is a clean modus-tollens on the specific market-link mechanism, valid conditional on the premise. Probed the acknowledged Weissman/Stoyan-Chiu defeater (residential-proximity ascertainment: case-finding concentrated at central hospitals near the market): this is a distinct mechanism from market-link ascertainment and does not deny the stated conclusion (which is scoped to “market-link” ascertainment); it is a separate, upstream bias priced against the relevant observation at step 8. The conclusion is correctly scoped and hedged (“not mere”/“supporting”), so no correction. Approved, checked.