# NormanPerlmutter comments on French long COVID study: Belief vs Infection

• “If we add all the percentage point increases (i.e. how many more percentage points serology positive participants experienced persistent symptoms vs serology negative participants—data from table 2) then we get 20.3%.”

I am not sure whether this reasoning is correct. It seems to be dependent on how the symptoms are categorized. For instance, suppose we divided fatigue into moderate fatigue and severe fatigue. The increased probability for each might be 5%, and then you would get 25.3% rather than 20.3%. Or suppose we combined fatigue and poor attention, which are likely correlated. The combined increased probability of “fatigue or poor attention” is likely less than 7.8%, and this would bring you down from 20%.

• Yes, I agree that some symptoms are likely highly correlated. I didn’t intend to rule out that possibility with that sentence—I was just trying to say how I did my math (although I’m not sure how clear I was!). The correct conclusion is in the following sentence:

So having COVID on average gives you ~0.2 persistent symptoms vs not having COVID, with presumably some people having more than one symptom.

Possibly it would be better to add the caveat “0.2 persistent symptoms of those symptoms investigated”.