Noted sociologist Richard Florida has an opinion piece in the Finacial Times and The Atlantic (see here) about how immigration may be responsible for the recent decline in violent crime in cities. Many explanations have been given for why crime has decreased since the nineteen nineties. The bestselling book Freakonomics suggested that the decline was because of legalized abortion, which meant fewer unwanted children who would go on to be criminals. Florida shows that there is a strong negative correlation between the presence of large immigrant communities and the crime rate. Again, like all epidemiological results, this correlation may or may not be significant much less have causal value. That is not to say that it is not correct. Immigrant neighborhoods may have a greater sense of a small town community that discourages crime but if the opposite correlation was found an equally plausible just-so story could also be concocted. I think the crucial point about this result along with all other explanations of complex phenomena is that we are drawn towards single universal explanations. I am all the time even though there may not be a reason why there should even be an explanation in a few hundred bits. The opposite view would be that a single explanation is implausible. After all, something like crime involves millions upon millions of degrees of freedom so why should it be compressible to a few hundred bits. However, if the phenomenon is consistent across many cities and regions then maybe a global explanation may be in order. The variance around the mean is also important. If the variability is low then a universal explanation carries more weight. I think that we tend to either embrace reduced descriptions or reject them outright based on the ideas presented. However, in many cases, a careful examination of the data may at least tell us if a reduced description is warranted or not.