Where does all the heterogeneity come from?

Here is a Christopher Balding tweet storm, excerpt:

Iceland has done almost 14k tests on an island of 360k so more than 3% of the total population…They have more than 800 confirmed cases, 10k people in quarantine, 800 in isolation, 18 hospitalizations, 6 in ICU, and 2 dead…About how many people SHOULD have corona if the spread etc numbers are accurate. As of March 27, Iceland would be expected to have more than 46k people that have corona. Emphasis this is on an island of 360k and 800 confirmed cases.

What is going on in the Icelandic numbers?  What accounts for this apparent heterogeneity?  Dosage?  Is it that Icelandic clustering is mostly in one easy to control central city and the rest already is “socially distanced,” even in the best of times?

I know there are some MR readers in Iceland, and presumably they read the Icelandic press.  Can anyone shed light on why the death rate is not higher in Iceland?  Is it that the death rate is about to burst a week from now?  Alternatively, you might think the Icelanders have kept their hospitals up and running — important for sure — but that doesn’t explain what seems to be a quite low rate of reported cases.  Or is it that Iceland’s second largest city is so tiny — Akureyri at 18,925 inhabitants — that the virus doesn’t have many easy chances to recirculate once cut off for a while?

Similarly, Sweden hasn’t restricted public life very much and they do not seem to be falling apart?

How much better is Staten Island (less dense) doing than Manhattan (more dense)?

Some reports indicate that in hard-hit Westchester County,. NY, the rate of hospitalization is about one percent (8-10 percent in some other places).  Alternatively, here is serious talk that the death toll in Wuhan is 20x official figures.

How much of the heterogeneity results from the kind of mixing you get?  One account of the low German death rate is the young and the old were never pushed together so much by the policy response.  One account of the high Italian death and hospitalization rate is that the initial quarantine was only regional and thus it spread very dangerous forms of mixing throughout the larger country.

It is possible that Cambodia, Thailand, and Vietnam still will be hit hard, but so far the signs do not indicate as such.  Warm weather may play a positive role, though that remains speculative.  The latest weather paper appears credible and indicates some modestly positive results.  Of course weather won’t explain the relative Icelandic and Swedish success, if indeed those are truly successes.

By the way, on the “everyone already has it” theory, a semi-random sample of 645 from Colorado showed zero positives.

So where is all this heterogeneity coming from?  Is it all just bad data?  That seems hard to believe at this point, and Iceland seems like a plausible source of reasonably good data.

As for concrete conclusions, these heterogeneities should make us more skeptical about any models of the situation.  But it would be wrong to conclude that we should do less, arguably risk-aversion could induce us to wish to do more, including on the lock downs front.

It is also worth pondering which heterogeneities are “baked in,” such as heat and age structure of the population, and which heterogeneities can be altered at the margin, such as forms of social mingling.  It is at least possible that studying these heterogeneities could make policy far more potent.

Overall, I do not see enough people asking these questions.