Poverty, Crime and Causality

I was bouncing around my twitter feed and landed on this tweet which in turn took me to a paper entiteld Childhood family income, adolescent violent criminality and substance misuse: quasi-experimental total population study. The paper appeared in the British Journal of Psychiatry in 2014. Here’s the basic summary:

Low socioeconomic status in childhood is a well-known
predictor of subsequent criminal and substance misuse
behaviours but the causal mechanisms are questioned.

To investigate whether childhood family income predicts subsequent violent criminality and substance misuse and whether the associations are in turn explained by unobserved familial risk factors.

Nationwide Swedish quasi-experimental, family-based study following cohorts born 1989–1993 (ntotal = 526 167, ncousins = 262 267, nsiblings = 216 424) between the ages of 15 and 21 years.

Children of parents in the lowest income quintile experienced a seven-fold increased hazard rate (HR) of being convicted of violent criminality compared with peers in the highest quintile (HR = 6.78, 95% CI 6.23–7.38). This association was entirely accounted for by unobserved familial risk factors (HR = 0.95, 95% CI 0.44–2.03). Similar pattern of effects was found for substance misuse.


Declaration of interest

Because the British (let alone the Swedes) seem incapable of doing proper American, it might be worth translating the paper into something we English speakers can follow. Here goes. The study looked at 526,167 Swedish kids, or about 89% of all kids born in Sweden from 1989 to 1993. (Kids were excluded from the sample if they died or emigrated before their 15th birthday, if they were born with birth defects, if they couldn’t be linked to their birth parents, or if the authors were unable to determine the parents’ level of income.)

The authors found (no surprise to anyone) that kids born into the lowest income twentieth percentile of the population are far more likely to get convicted of violent criminal activity or become substance abusers. But, by accounting for changes in a family’s income over time and how that affected (or didn’t) criminality and substance abuse outcomes of siblings and cousins, the authors were able to conclude that a family’s income was not associated with violent criminal activity or substance abuse except insofar as income was being driven by some other unobserved factor(s) that itself was associated with negative outcomes. That unobserved factor (or factors) runs in families.

The authors are not as clear as I’d like in describing the data adjustment, and the process they use is not one I have employed myself at any point.  But if I understand the limited description of the process correctly, they are basically noting that a kid in a 60th percentile income family is no less likely to become a criminal than his younger brother will be several years later when the family has dropped to below the 20th percentile of income.   Furthermore, within each income level, crime tends to run in families.

To take the paper’s findings a bit further, there is a serious implication here: it isn’t so much that poverty drives people into crime, but that families whose members have a tendency toward criminal behavior have an increased likelihood of ending up poor. Perhaps those who lack empathy are both more likely to commit crimes and less willing or able to behave in ways that allow them to get and retain good jobs. Of course, some of the smarter criminals can fake empathy enough to do quite well for themselves. It is also important to note that most poor people are not criminal. Nevertheless, the reason crime correlates with poverty is not that poverty leads to crime, but rather that for a not insignificant piece of the population, criminal tendencies are associated with traits that increase a person’s likelihood of being in poverty.


update…  grammatical error in the last line of the post corrected, July 7, 5:52 AM PST

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