The median household income in Middlesex is over $100K (that's where Harvard is located, right next to MIT). Incarcerations were also flat in Martha's Vineyard, but so what?

My priors say Middlesex wouldn't show increased rates of incarceration regardless of the amount of policing, the passage of three-strikes laws, the passage of the Clinton crime bill, etc. due to the demographics of the area. What do your prior's say?

Universality (to me) means "more criminals were incarcerated everywhere we expected them to be (based on demographics) and regardless of changes in local policies or funding, because there was a nationwide push to increase incarceration rates in the 90s." Do you mean something else by "universality"? Maybe we just disagree over definitions or something.

And yet, the crime rate in that county (and in Cambridge and Lowell) reflects the same plunging nature as the rest of the state and nation, since 1990 peak.

Take the big CSV from the github I posted, combine it with the FBI UCR data, and try to find a correlation between incarceration rate and crime rate.

I have, it's the main topic I study. I've just never met anyone with the view that increased incarcerations rates are not associated with decreases in crime (specifically, violent crime), and I don't think the data supports that either. I literally have no idea how you came to that conclusion given the stats available to researchers over the last 40 years.

I'm not suggesting that there aren't other ways to decrease crime besides incarceration, there are many possibilities. But I don't think there's any data showing that incarcerating criminals doesn't reduce (violent) crime.

So I'll just assume we agree in general, and that our definitions are different somehow, since we seem to be looking at the same datasets.

It’s clear that incarceration rates are associated with falling violent crime, to the extent that one went up and the other went down, but the existence of large jurisdictions that enjoyed the latter without the former casts doubt on the idea of causation.