This is extremely important to keep in mind with respect to that story about how we shouldn't have shut down the country that many, many people may are already be infected. https://twitter.com/cmyeaton/status/1246165232105525249

We have many sources of evidence from which to estimate asymptomatic infection rate. The studies above, Diamond Princess, etc. These indicate relatively low asymptomatic rates. (Of course there may be many uncounted *symptomatic* infections. Also worth having a better handle on.)