Agreed, when using the "deaths / (deaths + recoveries)" formula, recoveries being under-reported is possible and would skew the CFR upward. But also, if deaths are under-reported in the same proportion as recoveries, then it would not affect the CFR.
I suppose one way to reduce uncertainty is to examine a cohort of patients and follow it meticulously. To do that, we can look at the 99-patient case study published in The Lancet yesterday: https://www.thelancet.com/journals/lancet/article/PIIS0140-6... 11 died, 31 were discharged, and 57 remain in the hospital. This suggests a CFR of 11/(11+31) = 26% The assumption epidemiologists make when they use this formula is that the 57 still in the hospital have the same chance of dying as those who already died in the hospital.
I suppose one way to reduce uncertainty is to examine a cohort of patients and follow it meticulously. To do that, we can look at the 99-patient case study published in The Lancet yesterday: https://www.thelancet.com/journals/lancet/article/PIIS0140-6... 11 died, 31 were discharged, and 57 remain in the hospital. This suggests a CFR of 11/(11+31) = 26% The assumption epidemiologists make when they use this formula is that the 57 still in the hospital have the same chance of dying as those who already died in the hospital.