> That "we don't know much" nuance rarely makes it into short articles. Well it made it into this one: Click on my post from last year to get more details abo

> That "we don't know much" nuance rarely makes it into short articles. Well it made it into this one: Click on my post from last year to get more details about both the strengths and weaknesses of this paper. As with any retrospective study like this, there are reasons to be cautious about the results. Clicking the link gives us a pretty nuanced discussion: On the negative side, it's risky to look solely at homicide numbers. This is because the absolute number of murders is small, especially on a city-by-city basis, and that means there's a lot of noise in the numbers. This is especially true when you're limited to a period of time as short as 15 years. There's also the fact that this was an era when lead paint was widely used, and that's very hard to tease out from the use of lead in pipes. Finally, there's the usual problem of any study like this: what do you control for? The use of lead pipes is plausibly unrelated to anything else related to crime, but it's impossible to know for sure. The authors do control for black population, foreign-born population, occupations, home ownership, and gender breakdown, and that reduces their effect size from 11.4 percent to 8.6 percent. Might some other control reduce it even further? Plus there's the anomaly of Southern cities. Very few of them used lead pipes, but some did, and their murder rates were essentially no different from any other Southern cities. Why? It's possible that this is because their use of lead pipes was small (F&M have data on lead pipe use by city, but not on how much lead piping was used in each city). But it's still odd.