‘Causal’ is not enough
Yesterday’s post about crime rates and liquor stores was tagged ‘correlation vs causation’, but it’s more complicated than that. It’s not even clear what sort of causation is at stake.
I think we can all agree that being drunk, like being young and male, is a causal factor in violent crime. But that’s not the question. There are two possible causal stories behind higher crime rates near liquor stores, or, more precisely, alcohol licenses. These are truly causal alternatives to the skeptical argument that it’s actually (demand for) drinking that leads to alcohol licenses.
The weaker causal story is that people get drunk, and when they do, they are more likely to do it nearer to alcohol licenses. That’s certainly the case for pubs and restaurants — if you buy beer from a pub, you are going to be drinking it at the pub — and could be true for liquor stores as well. This story would say that if you moved an alcohol license the crime would move, and if you shut down one place, the drunkenness and crime would relocate among the available options. If this is true, it’s useful to local community groups wanting to improve local conditions, but it’s pretty much useless from a public health and safety viewpoint.
The stronger story is that people won’t drink if they have to go further to get alcohol, so that reducing the number of licenses will reduce drinking. On this theory, reducing licenses could have a health and safety impact beyond just local redistribution of crime.
It’s not possible to distinguish these using the available data. There’s good evidence that something like the first story holds for CCTV installation — it pushes crime out of the surveillance zone but doesn’t stop it. And there’s some evidence that something like the second explanation works for stopping kids from smoking — adding inconvenience and cost has much more of an impact on them than on adults.
Thomas Lumley (@tslumley) is Professor of Biostatistics at the University of Auckland. His research interests include semiparametric models, survey sampling, statistical computing, foundations of statistics, and whatever methodological problems his medical collaborators come up with. He also blogs at Biased and Inefficient See all posts by Thomas Lumley »
I’d suggest another theory, that dairies are the problem. You see, all we have here is that serious crime is associated with proximity to licensed premises. I’d be willing to bet there was a very similar relationship to dairies, as most licensed premises are located near dairies. The underlying issue may well be that urban and suburban centres are associated with serious crime. Which might relate to your earlier theory that there might be more people near those centres, including those who don’t live nearby. The full paper is available at http://onlinelibrary.wiley.com/doi/10.1111/j.1753-6405.2012.00827.x/abstract
If you read that paper, you’ll see that population density is a very important figure in the crimes data.
13 years ago
Table 1 of the paper presents the number of alcohol outlets and number of usual residents. The ratio of residents/outlets is fairly constant (490~500) for quintiles 1 to 4, reducing to 332 for the highest population density quintile 5, which probably has the highest floating population as well. I wouldn’t be surprised that once you add the floating population the ratio would get closer to 500.
13 years ago
I wish I could remember where it was, but I do recall reading, a couple of years ago, an analysis of the zero tolerance policies that were put in place in New York some time ago. iirc, they tracked crime in both the New York boroughs that had the zero tolerance policies and the surrounding suburbs. Again, iirc, total crime didn’t go down, it moved.
The second, stronger causal story should be able to tested. get a community with high crime/high number of liquor outlets, shut down some of the outlets of normalize for per head of population or something, track the crime in both that suburb and it’s surrounding ones.
oh for some evidence based policy.
13 years ago