> So what do you think explains the difference between Japan and NY?

There are a thousand factors but my bet is that Japan experienced SARS firsthand and just like South Korea or Vietnam, they learned their lesson. It became the epidemic case study for public health officials and doctors in the entire region (and Canada). Regulators went out of their way to make reporting easy and doctors were all trained to look for and treat viral respiratory diseases early. Wearing masks went from being an oddity to wide spread cultural acceptance. For those reasons, you can't compare the effectiveness of measures in California to those in Wyoming using Japan as a measuring stick.

There are far more differences between Japan and California than there are between California and Wyoming. The latter share their language, the majority of their healthcare regulations, political differences, the CDC, and so on. Right now, traveling from Japan to Wyoming is practically impossible but traveling from California to Wyoming is a medium length road trip or one hop in a a tiny plane with zero enforceable travel restrictions.

> Even if Japan's death count is understated, there is zero chance that all of Japan's medical staff and press have somehow failed to notice and report NYC-level mortality.

I'm not an expert on Japanese culture but I've got enough first hand experience to know that is a failure of imagination and the definition of false confidence. Read about Tepco, the Japanese nuclear regulators, and the series of unfortunate events that led to Fukushima containment failures. It was a systemic failure that shares many parallels to Japans's coronavirus response.

> And I'm not sure what you think is my "false confidence about Japan's comparability to the US"? I certainly don't believe Japan's response would work equally well in NY, considering that NY applied stricter measures and ended up with 200x the death rate.

You (imo) falsely believe that Japan's death rate is accurate (let's wait a few months for accurate general morality). You also falsely believe that their death rate can be used to draw conclusions about the effectiveness of measures in the United States. I'm not sure about the former but certain about the latter. New York had "stricter" measures based on cultural expectations that were practically cultural norms in Japan. There is simply no baseline or control group possible between the two demographics.

> I'd guess these factors explain much more of the variation in mortality by region than variation in the governments' responses, though I'm not sure.

There is less variation within nations than there is between them. That's why they became nations instead of going to war amongst themselves (modulo some geopolitics that apply to the Middle East and the Balkans, not Japan).

> And you're missing my point about deaths per capita. That's an intrinsically meaningful number, because people care about the probability that they die (or get seriously sick, etc.). Other numbers are valuable only to the extent they predict that. Population density is one input, but it's clearly not the only factor, and your simplistic focus on that isn't useful.

People care about ending the quarantine. The quarantine will end based on public health policy. Public health decision makers aren't basing their decision on deaths per capita, they're basing them on localized deaths per capita, which depends on the density in each city, metropolis, and states.

I honestly don't even know what point you're trying to make. Are we trying to end the quarantine or are you trying to make some ideological point?