That's ridiculously bad. In effect their logic is: "We controlled for various things in the original regression, but hey, there still could be unmeasured confo

That's ridiculously bad. In effect their logic is: "We controlled for various things in the original regression, but hey, there still could be unmeasured confounders that make people who got COVID score less on IQ tests, even before they got COVID! (Like coming from a poorer background, other health vulnerabilities etc. etc. etc.) Unfortunately, we don't have a measure of IQ from before they got COVID. So, we estimated one using a set of variables that we do have measures for!" Erm... if those extra variables predict IQ, then why not just add them as controls? And of course, if you do so, then you'll still hit the problem that there are plenty of potential unmeasured confounders out there. This is just a silly way to pretend you've controlled for something, when in fact you can't. The quality of statistics in medicine is so bad. Disgracefully bad. In particular, the Lancet seems to be a serial offender.