I believe that the Santa Clara (Stanford) and the LA County (USC) studies getting so much news the last few days are both pretty junky and should not be used as evidence of anything in particular. There's a lot of data around the world pointing to about a 1% fatality rate (across an average demographic sampling, without an overwhelmed health care system), so we should be pretty darn skeptical of a 0.18% estimate. The major news media is doing a terrible job at being skeptical about this right now, so here are some other sources.

The two main issues with the Santa Clara study are 1) the false-positive rate, and 2) the non-random sample. Here's a (warning: long) thread from a former virologist who is now a VC and "pop sci translator" type of writer, which after the extended metaphor discusses both of those issues: https://twitter.com/PeterKolch.../status/1251585935994740736

Here's a more focused analysis of issue #1 - given the sensitivity of the test, up to *all* of the positives *could* be false positives: https://twitter.com/jjcherian/status/1251272333177880576

And here's one that talks more about who they tested. They recruited people on Facebook to enroll in the study, so they likely got self-selection bias from people thinking "I think I might have had it, I want to get tested". https://twitter.com/nataliexdean/status/1251309217215942656

Finally, here's a slightly-older thread from my current-favorite local scientist, explaining why we can have a very high confidence that the virus wasn't running wild in CA before Jan: https://twitter.com/trvrb/status/1249414291297464321 There are two ways we know: A) they were able to test thousands of Flu Study samples from Jan/Feb for Covid19, and B) the known genetic mutation rate from hundreds of gene sequencings of the virus.
There are other common coronaviruses and rhinoviruses, and perhaps even a particularly nasty one that hit a bunch of people around here earlier, but there isn't evidence that those were Covid19. The WA spread came from a Jan 15-21 person travelling from China, which led directly to the Kirkland nursing home outbreak detected in late Feb.(The news of a Feb 6 death in CA does not seem to, IMHO, license a major revision of the spread/prevalence estimations - everyone thinking "I got sick in December, maybe I had it" should remain very skeptical.)

As for LA versus Santa Clara... "The Santa Clara study that used some of the same researchers as USC was heavily criticized for its methodology, which recruited volunteers on social media. The test it used — the same one used by USC — was criticized as unreliable for producing false negative or positive results." https://www.seattlepi.com/news/article/Los-Angeles-study-suggests-coronavirus-much-more-15213930.php

There's also been a claim of another source of potential false-positives, where this particular test confounds some other similar virii: https://twitter.com/rafalkonopka/status/1252579687974477825

Some news stories say the LA study did better than Santa Clara by using an independent vendor's database to recruit participants, however the LA Times reports otherwise: https://twitter.com/yellingatwind/status/1252363747156389889

One more thread on the specificity rate evidence: https://twitter.com/jjcherian/status/1252716921629409282

In short: LA study doesn't really seem to provide any more independence to the evidence, i.e. the same flaws could be present in both.

I don't want to claim that their data *is* all false-positives, by any means. It seems likely that there may be 10-15X the number of real cases as detected cases... just not 50-85X. The math on such a high multiple would imply that more-than-100% of NYC would had to have had the virus in order to produce as many deaths as they've had.

In my dream world, these studies' surprising results would get replicated by others quickly and then we'd discover that there's some heretofore completely undetected low-impact version spreading in the west coast states... but I don't have high hopes of that.

4/24 Addition: New York reports its own study: https://www.nytimes.com/2020/04/23/nyregion/coronavirus-antibodies-test-ny.html  That estimates a more plausible 12X ratio: https://twitter.com/nataliexdean/status/1253472799315963904 and an IFR somewhere around 1%: https://twitter.com/trvrb/status/1253398325245603840