Murder Rates: Depends on where You Measure

When I hear about city murder rates, I always wonder whether that refers to the city proper, or the greater metro-area. City murder rates are usually higher because suburbs tend to be safer. But city borders can be arbitrary- when considering two similar metro-areas, one city could have larger borders, which then makes it appear safer because it includes more suburban-type neighborhoods. To help clear this up, I used FBI data to graph the city murder rate versus the murder rate for the entire metropolitan statistical area (MSA):



New Orleans is the clear outlier. Detroit, Baltimore, and St. Louis have similarly high murder rates in the city, but New Orleans has a uniquely high murder rate for the MSA. The murder rate for the greater metro area of New Orleans is about as high as the city of Memphis or Atlanta (unlabeled).

The trend line shows the average relationship between the city rate and the MSA rate. Virgina Beach is noticeably above the trend line, but that is because the Virginia Beach MSA is a combination of multiple cities, including the less-safe Norfolk and Newport News, unlike most other MSAs which tend to be a single large city and surrounding suburbs. 

In each case, the largest city by population in the MSA is graphed, and only MSAs with at least a million residents are included.

The same graph is reproduced below as an interactive, which provides hover text for unlabeled cities:

The relationship between city murder rate and MSA murder rate is fairly strong (R square = 0.57). But this is at least partly driven by the inclusion of city rates in the MSA rate. The graph below shows city rate and the non-city rate- the MSA rate minus the murders and population from the city.

Notice there is almost no relationship between city murder rate and suburb murder rate (R Square = 0.02).

Cities lowest on the graph and to the left have the safest suburbs relative to the city. Milwaukee's murder rate is the most segregated along city borders- a person in the city is 28 times more likely to be murdered than a person in the metropolitan area outside of the city.

*Some MSAs did not have all member cities/municipalities report crime data. In these cases, I used the FBI's estimated totals. All cities had reporting for at least 94% of their population, with the exception of Indianapolis (86%).