I also have questions. 1. What would account for the uninfected seemingly becoming "smarter" in the quarantine period? 2. What would account for both groups appearing to decline significantly after 90 days? No, you're not reading it wrong. Both your questions reflect the unreliability of unblinded self-assessments. Your first question suggests the number of people in the study group was too small. Is that a real difference, or would these apparent differences go away in a larger group? Your second question about the significant decline in both groups after 90 days, suggests how big a factor motivation played in these self-assessments. After 90 days it might have been too boring to perform those same tests again.