Previously I posted on the telling fact that the percentage of a state's population that is black and Hispanic reveals more about that state's rate of violent crime than a host of other variables combined. Mping, who runs the Fat Knowledge blog, threw out some devil's advocate factors to consider. I haven't been able to find anything on police per capita (please let me know if you are aware of available data). Some factors suggested that I did take a look at and their respective correlations with a state's rate of violent crime:
% of population using illicit drugs in the last month: .130 (not significant)
% of pop between ages 18-24: .185 (not significant)
Median age: .173 (inverse) (not significant)
% of households containing one male, no spouse, and no children: .541
% of single-mother households: .699
The first three are all outside reliability at 90% confidence, but the loose correlations they have with violent crime trend in the direction that conventional wisdom asserts they should (more drug use and more 18-24 year-olds means more crime, the older the state's population the lower its criminality).
Both measures of household composition are statistically significant, again trending in the expected direction. When men assume more responsibility, they tend to get into less trouble. This is an argument for policies that make housing prices affordable enough for men to raise families and make a monthly mortgage payment. Our immigration policies appear to do the opposite, however.
The lack of a father figure removes a traditional disciplinary figure from the equation. Single mothers, around 60% of whom are impoverished, must pull double-duty. When a male child reaches early adolescence, he is physically unchallenged by mom. The staggering increase in out-of-wedlock births over the last forty years is yet another tragic legacy of the most socially disastrous decade of the US' existence, the sixties. Propensity to commit violent crime is only one of several sad circumstances for children in this situation. But with an r of .699, it is a very real relationship.
Still, it's not as strong a predictor as the percentage of the population that is either black or Hispanic (r = .800). Antero Kalva tells me that at the county level the percentage of single-mother households trumps the percentage of the population that is black or Hispanic in predicting violent crime, rendering the latter statistically insignificant when single-mothers are included.
Unfortunately I'm not a prospective PhD student working on a dissertation so the thought of entering data for 3,140 counties is daunting. At the state level, controlling for race eliminates the statistical significance of single-mother households. Moreover, the percentage of the population that is black or Hispanic is a more powerful predictor of violent crime (recall r = .800) than the following factors combined: % single-mother households, % single-male only households, % of the population using illicit drugs in the last month, % of the population between 18-24, median age, poverty rate, % of the population with a bachelor's degree, % of the population having completed high school, the gini coefficient, the rate of gun ownership, and the rate of unemployment (combined r = .784).
The correlation between single-mother households and the percent of the population that is black or Hispanic is .829, affirming that the two serve as proxies for one another, as an anonymous commenter suggested (especially for blacks, where the correlation is an even higher .875).
Why would the 'causal' factor be single-mother households at the county level and race at the state level? The sheer number of counties that have almost no black or Hispanic population strikes me as the most plausible explanation. Since Antero presumably did not adjust for county population size, the bulk of the data examined will have been from Bush Country. As there is almost no black or Hispanic population to speak of in most of these counties, other non-racial factors move in to fill the gap for the whites living in them. Well, excluding race, the percentage of single-mother homes is the only factor that retains statistical significance when the others previously listed are included. So in places like, say, all of Kansas west of Topeka, single-mother households are probably the critical factor.
I wonder what the relationship looks like if only counties where the population of blacks and Hispanics comprise at least 5% of the population are included. Antero, if you are running your numbers on SPSS, this should be easy to find out (as I once again tell myself I need to get the full version so I can enjoy more statistical alacrity than Excel allows for). This would address the issue of race without artificially crippling it as an explanation by including data from counties from which it cannot be a factor because it doesn't exist (since the pertinent policy question has to do with the US' shifting racial composition).
An interesting aside: perusing through The Color of Crime, the criminality of Native Americans stuck out (see p9). Including the percentage of Native Americans with blacks and Hispanics and then correlating with violent crime, the r creeps up to .810, a seemingly trivial but actually rather substantial increase when it is considered that only 1% of the US population is Native American.
++Addition++Antero sent me his county level data and, as he said, the percentage of single mothers is a better predictor of violent crime than racial data.
A couple of interesting things: the correlations between crime and a host of factors, including race and single mother households, are much weaker on the county level than on the state level (% single mothers, for example, for the 2,702 counties with complete racial and criminal data sets, correlates with violent crime at .538 compared to .699 statewide; % black and Hispanic correlates with violent crime at .428 at the county level and .800 statewide). Thus, even as the apparently strongest single predictor of violent crime, the percentage of single mother households still only 'explains' less than 30% of a county's violent crime rate. In contrast, knowing the full racial composition of a state explains 70% of that state's violent crime rate.
Perplexing. I would expect the relationships to become progressively weaker, not stronger, as the source of data broadened. Maybe there are dilution effects on a local level that become neutralized on a larger level (like the effect of immigration on wages in local economies compared to its effect on the national economy), although I can't readily conceive what the causation would be. Also, there are many missing data on the county level. For example, New York (the highest population density in the nation), Bronx, Richmond, Cook (Illinois), and Queen counties all do not have violent crime data, and they represent a considerable number of people (twelve million) in rough areas of the country that are not being factored into the county level analysis (but presumably are included in the FBI statistics).
In any case, more reason to lament the breakup of the nuclear family and re-stigmatize illegitimacy.