Yeah I mostly agree, was trying to be polite.

They included a surgeon control variable in their model.

https://www.bmj.com/content/bmj/371/bmj.m4381.full.pdf

Yes, they say they did all this (and much more) in secondary analyses. I'm curious how does one find the eTables supplementary information ?

Edit: nevermind, found it: https://www.bmj.com/content/bmj/suppl/2020/12/09/bmj.m4381.D...

Edit 2: it looks like solid, peer-reviewed research

Ah, couldn't access the page so had assumed parent was correct reporting that they hadn't done this control. Sorry for getting that wrong - won't trust similar posts in the future.