Hatzenbuehler’s work is the latest in a growing trend of applying methods from the health sciences to complex social problems. Several public-health researchers have reasoned that contagion is an appropriate analogy for incarceration, due to the well-documented finding that proximity to an incarcerated (or “infected”) individual greatly increases the likelihood of incarceration. Ernest Drucker’s landmark A Plague of Prisons was the first mainstream work to apply epidemiological modeling to the problem of mass incarceration in order to trace its path through populations. Drucker created a profile for the disease, pointing out that young minority men are the most susceptible, making up more than 30 percent of the cases; poor urban neighborhoods are the hardest hit, with some communities having an infection rate of up to 90 percent; afflicted individuals are often socially marginalized and incapacitated for life, unable to find stable employment or housing; and the children growing up in affected families have shortened life expectancies and are six to seven times more likely to be infected than are children in unaffected families.

Others continue to strengthen the case for why incarceration is in many ways similar to a plague. Last fall, researcher Kristian Lum and others from the Virginia Bioinformatics Institute used a susceptible-infectious-susceptible (SIS) model of infectious-disease propagation to explain why even moderate differences in sentence length can cause the vast racial disparities observed in the aggregate prison population. An SIS model is nonlinear: The number of infected individuals and the number of transmissions are not proportional, due to feedback loops present as people transition between being infectious (incarcerated) and susceptible (out of prison, but at risk of going back).

The researchers in Lum’s study began by considering a puzzle in the data: The per capita rate of incarceration almost quadrupled between 1978 and 2011, and mostly affected African Americans. However, the authors note, “the increase in imprisonment of black males since 1980 was not matched by a similar increase in black-male criminality.” Their model considered incarcerated individuals “infectious” to those who are most affected by their absence, and adjusted the “transmission” probability according to relationship type and personal characteristics (children and male associates being the most susceptible). When individuals are released from prison, they return to a “susceptible” state, while their newly incarcerated friends and relatives introduce positive feedback into the system by becoming the source of additional infections. These feedback loops are responsible for the explosive transmission rate that continues to amplify racial disparities.

According to the Bureau of Justice Statistics, whites have a mean sentence of 14 months for drug possession, while blacks have a mean sentence of 17 months for the same offense—extending the infectious window by three crucial months per individual. Despite these enduring differences, Columbia’s New York Psychiatric Institute used large national data sets to demonstrate the lower rates of drug offenses and use for blacks versus whites in the United States. Applying epidemiological tools to the problem adds urgency to the argument for reform. The implications are clear, Lum and her fellow researchers write:

If incarceration risk is indeed propagated through social networks, our results predict that incarceration is self-perpetuating and changes to sentencing policy may have long-term unanticipated consequences. Indeed, harsher sentencing may hinder progress towards the intended goal of decreasing crime, creating safer communities and maximizing justice to the state, victim, and offender. Our model suggests that increased sentencing for an individual has negative effects that spread through social networks to affect families and whole communities. As a consequence, increased sentence lengths may create criminals from individuals who otherwise would have avoided criminal behavior.

These patterns reveal new depths of the incarceration-poverty problem, with health effects that may carry over into new generations alongside the related economic burdens. The cumulative emotional stress resulting from high incarceration rates in a community may generate feedback loops of its own—perhaps by inducing substance abuse and other behaviors associated with depression and anxiety, and in turn predicting further incarceration.