That's not their scope of analysis, that's just the introductory sentence. It's meant to reflect on the existing body of knowledge prior to their study. To para

That's not their scope of analysis, that's just the introductory sentence. It's meant to reflect on the existing body of knowledge prior to their study. To paraphrase, it's essentially saying "this is what we know already, and here is what we're adding to the body of knowledge with this study" As always, it's best to read the source material directly but these are relevant excerpts from the abstract : "Case studies have revealed neurological problems in severely affected COVID-19 patients. However, there is little information regarding the nature and broader prevalence of cognitive problems post-infection or across the full spread of severity... ...People who had recovered, including those no longer reporting symptoms, exhibited significant cognitive deficits when controlling for age, gender, education level, income, racial-ethnic group and pre-existing medical disorders. They were of substantial effect size for people who had been hospitalised, but also for mild but biologically confirmed cases who reported no breathing difficulty." The last part directly contradicts the idea that this study is limited in scope to severe cases.