Communities experiencing growing levels of income inequality are at a heightened risk for mass shootings, according to a study in the upcoming December issue of the BMC Public Health Journal.
Although analyses of mass shootings, commonly defined as incidents involving three or more victim-related injuries, usually focus on the troubled mental health of individual shooters, the authors of the study argue that “hostile social environments” created by a shift in a community’s socioeconomic profile can be a critical factor.
An analysis of such shootings between 1990 and 2015 suggests that they are “more likely” to take place in “counties with growing levels of income inequality,” wrote co-authors Roy Kwon, an associate professor of sociology, and Joseph Cabrera, an assistant professor of sociology, both at La Verne University.
“The clear conclusion from our results is that socioeconomic factors, such as income inequality, are the main driver of mass shootings in the United States,” they wrote.
The authors build on previous research that found a positive association between levels of inequality and mass shootings.
They noted that the number of such incidents has increased from eight in the 1970s to 115 through the current decade by the end of 2015.
During the same period, roughly, the income gap in the U.S. has widened: The income of the top 0.1 percent increased by 4 percent annually between 1980 to 2011, while the income of the bottom 99 percent increased by only 0.6 percent annually from 1976 to 2007.
Existing research has shown that income inequality “can produce an unstable and hostile social environment,” according to the authors.
“An important question thus remains unanswered in the empirical literature: Is the contemporary growth of income inequality associated with the recent rise of mass shootings in the United States?”
According to the authors, their study expands on broader research regarding the relationship between income inequality and aggression, including crime and homicide rates.
The new study focuses on the interaction between income and inequality and its relationship to mass shootings, instead of simply correlating it with levels of inequality, which was the focus of the authors’ previous studies in 2017 and 2018.
Using median household income data from the U.S. Census Bureau, the authors set out to determine the change in inequality levels of 3,144 U.S. counties from 1990 to 2015 in 10-year periods, with an additional seven control variables such as poverty, population density and unemployment rate.
Mass shooting data were drawn mainly from the Mass Shootings in America (MSA) data set at Stanford University, as well as data sets created from reportage in Mother Jones and USA Today.
Preliminary results show counties that experienced a steady rate of income inequality experience suffered five times as mass shootings than those which experienced a decrease in income inequality; counties that experienced an increase in income inequality experienced nearly six times as many.
The main results of the study calculated incidence rate ratios (IRRs) for each variable using a negative binomial regression, a type of distribution method commonly used for rare events, like mass shootings, for example.
Using the MSA criteria that defines a mass shooting as an incident resulting in three or more injuries, the study found “counties that experience one standard deviation increase of inequality will observe approximately 0.43 to 0.57 more mass shootings,” indicating a significant positive association.
These IRRs are not attached to specific occurrences of mass shootings, but are relative to the relationships between counties.
The strongest association by far was found between mass shootings and minorities as a percentage of the population. This finding was consistent with the authors’ previous research that detailed the myriad factors suffered by minority communities which lead to elevated crime rates.
The study references work by other sociologists, particularly Robert Merton, who was the first to advance “Strain Theory” in the 1930s. The theory posits that lack of opportunity and relative deprivation foster environments of resentment and hostility, and can be manifested in what’s called “goal blockage” —leading in effect to high degrees of frustration that can influence susceptible individuals.
Observing that poverty did not yield as strong an effect as income inequality in their results, the researchers included poverty as a separate variable to “ensure that the link between income inequality and mass shootings is due to relative differences of income and not the result of resource scarcity.”
Some caveats to the study, noted by the authors: much of the data is taken from media reports, which likely aren’t completely comprehensive; Internet access was limited in the 1990s, which could have affected the number of incidents reported during that time; and the dataset does not include gang- and drug-related shootings.
The authors acknowledge that most studies of mass shootings concentrate on the perpetrators’ state of mental health.
“However, there is reason to be skeptical of this proposed causal connection, especially since less than 5 percent of all firearm killings are attributable to those with mental illness, a proportion that translates to a rate that is lower than the national average for those without a mental illness,” they wrote.
Drawing on the policy implications of their findings, they add, “It may be prudent for academics and policymakers to identify policies that increase general social welfare in order to solve the mass shootings epidemic in the United States.”
Dane Stallone is a contributing writer to The Crime Report. The complete study is available here.