Cognitive deficits in people who have recovered from Covid-19
This Study suffers from at least one significant methodological flaw. They did not evaluate the same individuals pre- and post Covid infection but instead evaluated people as a group who were either previously infected or not. While they did try to correct for some socio-economic factors such as age their data did not allow them to factor in the socio-economic discrepancies in the distribution of early Covid cases which overwhelmingly hit service industry workers with direct customer exposure. People with Graduate Degrees were much more frequently able to self isolate and work from home than people without a high school equivalent degree.
What I find to be quite sad, is the fact that these researchers were actually in a position to retest a subset of the original test takers as more than 10% completed a follow up survey in December 2020 which surfaced 275 individuals who had contracted Covid after their first participation in the study.
Retesting those, as well as the >8000 individuals who had no change in Covid status to control for increase in age, increase in points due to getting better at the test with repeated exposure etc, would have been a sufficiently large dataset to actually confirm or rule out at least large effect sizes.