Ecological fallacy in the ranking of preceding procedures: a gender-structure consideration

Correspondence to: Xue-Lei Zhan (email: 13936629256@126.com)

Department of General Surgery

the First Hospital of Harbin

Harbin 150001

Heilongjiang

China

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BJS, https://doi.org/10.1093/bjs/znag025, published 07 May 2026

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We read with great interest the study by Gielen et al.1 on autoimmune disease (AID) after mesh hernia repair. The propensity-matched cohort of 3,000 patients is solid work, and the main finding—no difference in AID incidence between mesh and non-mesh groups—is what most surgeons would expect from short-term follow-up. But we are concerned about how Table 3 is used in the Discussion.

Table 3 shows inguinal hernia repair ranked 18th (0.50%) and cholecystectomy 9th (0.65%) among procedures before AID diagnosis. The authors take this as evidence that hernia repair is not over-represented. We think this reading misses something basic: the ranking is driven by who gets these operations, not by whether the operation causes AID.

Patients with AID are mostly women. Systemic Lupus Erythematosus (SLE) is about 9:1 female, Rheumatoid Arthritis (RA) about 3:12. Inguinal hernia, on the other hand, is a man's disease—86% male in this cohort. So, of course, hernia repair ranks low in an AID population: there are very few women in the hernia group to begin with, and women are the ones who get AID. The low ranking says nothing about mesh safety; it only says women don't get inguinal hernias. Cholecystectomy ranks higher because women get gallstones too, not because removing the gallbladder causes autoimmunity.

This is structural confounding, not a fair comparison3. The ranking mixes up baseline disease patterns with surgical risk. Table 3 cannot stand on its own as supporting evidence.

We suggest two things. First, the Discussion should make clear that Table 3 is limited by sex imbalance and does not independently support the null finding. Second, any future backward analysis should report sex-stratified rankings, or at least note which procedures are sex-skewed before interpreting the numbers.

This does not take away from the main matched analysis. But, without this caveat, readers—and surgeons counselling patients—may give Table 3 more weight than it deserves.

We thank the authors for this important contribution.