When you break it down that way it's a less strong correlation, but tends to support a model based on 'network effects' (opportunity) and/or social pressures (density).

It would be really interesting to slice things and compare relative rates for neighborhood level housing density, poverty/affluence, and education.

As a potential control study though, I'd like to propose focusing on quality of housing and 'tranquility' factors. How well does that housing prevent problematic interaction? (Noisy / smelly (air pollution of various kinds) / resource conflicts) My hypothesis is that higher quality housing and housing codes can contribute to decreasing stress. The need to build more housing to fulfill the more lofty living requirements would also have a positive effect on the affordability of housing (and naturally for the experiment would need to be targeted across all levels of need). Of course to eliminate the effect of housing merely being new at least some units would have to be new but built to the existing standard's minimums rather than the study's re-defined minimums.