The main study which backs up his guess is the report from the WHO's trip to Wuhan, where they actually did what was suggested above and mass-test random samples from the population, finding a very low incidence of positives. Personally I would find the WHO on a trip to China as not the most reliable of sources, so take it with an enormous grain of salt. But it's one data point.
Meanwhile, your link in [0] flat-out says we don't know the percent of asymptomatic cases. It is well-documented they exist. I have also seen some papers estimating the percent of cases that are asymptomatic as well under 20%, and as high as the 80-90% range, the difference between them making an enormous difference to the implied mortality rate.
A month ago, people pointed to South Korea's 0.5% fatality rate, a country which tests very aggressively, as an indication that the true fatality rate is much lower. Well, they still test just as aggressively, and now their mortality rate has risen to 1.96%. The disease started spreading in a population that skewed young there, and but now the disease has started to hit older demographics who have a much higher mortality rate. And of course, "asymptomatic" cases can also mean pre-symptomatic cases, as happened with the Diamond Princess, which had an observed 46% of positive cases be asymptomatic...only to have this rate fall to ~17% later.
Yeah basically the extreme correlation of mortality with age makes it hard to state a mortality rate. Small changes in the population age distribution create big changes in mortality.
Meanwhile, your link in [0] flat-out says we don't know the percent of asymptomatic cases. It is well-documented they exist. I have also seen some papers estimating the percent of cases that are asymptomatic as well under 20%, and as high as the 80-90% range, the difference between them making an enormous difference to the implied mortality rate.
A month ago, people pointed to South Korea's 0.5% fatality rate, a country which tests very aggressively, as an indication that the true fatality rate is much lower. Well, they still test just as aggressively, and now their mortality rate has risen to 1.96%. The disease started spreading in a population that skewed young there, and but now the disease has started to hit older demographics who have a much higher mortality rate. And of course, "asymptomatic" cases can also mean pre-symptomatic cases, as happened with the Diamond Princess, which had an observed 46% of positive cases be asymptomatic...only to have this rate fall to ~17% later.