Scientists have identified a strong link between increasing poverty, income inequality, and the rise in homicide rates across the United States. The study, encompassing data from 1990 to 2020, reveals that states with the highest levels of poverty and income disparity experienced the most significant spikes in homicide rates, especially notable during the turbulent year of 2020. The findings have been published in Evolutionary Human Sciences.
Previous research in the realm of sociology and economics has long attempted to untangle the complex web of factors contributing to homicide rates. Numerous studies have pointed towards various causes, ranging from socio-economic conditions to environmental factors. However, what remained elusive was a comprehensive analysis that could systematically account for the interplay between economic conditions like poverty and inequality, and their impact on violent crime, particularly homicide. This gap in understanding motivated the current study, aiming to explore the relationship between these socio-economic factors and homicide rates using a more nuanced approach.
“As homicides rates spiked during the 2020 COVID-19 pandemic, news outlets were nominating a host of potential causes to explain the increase, including factors such as ambient air temperature and city greenness,” explained study author Weston McCool, a postdoctoral fellow in the Society, Water, and Climate Research Group, and the Anthropology Department at the University of Utah.
“We were convinced, and still are, that the causes of the 2020 spike were related to the same underlying factors that have been structuring US homicide rates for decades, namely, poverty and inequality. We were also worried that without a theory of behavior, scholars would struggle to distinguish causal factors from spurious correlations or correlated effects. We wrote this paper to build on existing theory and to evaluate whether poverty and inequality can account for variation in homicide rates across US states over the last 30 years, including the 2020 spike.”
The researchers compiled and analyzed data for each U.S. state over a thirty-year period, from 1990 through 2020. They used homicide data from the FBI’s Uniform Crime Reporting Program and socio-economic information (specifically regarding poverty and income inequality) from the American Community Survey conducted by the U.S. Census Bureau. Notably, the Gini Index, a measure of income distribution within a state, was employed to assess income inequality. The study involved a comprehensive analysis of these datasets, looking for patterns and correlations over time and across different states.
From 2019 to 2020, an alarming increase in homicide rates was observed in 46 states. This period also saw a rise in the proportion of households living below the poverty line and an increase in income inequality in most of these states. Through sophisticated statistical modeling, the study demonstrated that poverty and inequality independently and jointly contributed to higher homicide rates. States with the highest levels of poverty and income inequality were found to have the highest homicide rates. This pattern remained consistent over the three decades of data analyzed.
“Typically, inequality is seen as the prime driver of homicide rates in the United States,” McCool told PsyPost. “Poverty is usually seen as a relatively less important causal factor, with some scholars dismissing its effects entirely. In our statistical model, we show that while inequality and poverty have strong independent effects on homicide rates, we were surprised to find that murders peak when and where inequality and poverty interact. That is, homicide rates peak when and where poverty and inequality have combined effects, which is a novel finding that we did not entirely anticipate.”
“Readers should come away with two related points: 1) As predicted by theory from the evolutionary social sciences, the combination of poverty and inequality predict homicide rates in the United States over the last 30 years (the range in which homicide data are available), including the 2020 COVID-19 spike. 2) Homicide rates disproportionately impact non-white communities due to a long history of systemic racism towards racial and ethnic minority groups that restrict individual’s access to resources and opportunities,” McCool explained. “We suggest these results provide compelling evidence to expand strategies for reducing homicide rates by dismantling structures of systemic racism that generate and concentrate sustained poverty and economic inequality.”
However, the study’s findings come with some caveats. For instance, the model used could not account for all the variations in homicide rates, leaving about 50% of the variation unexplained. This suggests that other factors, possibly cultural or institutional, also play a role in influencing homicide rates. Additionally, the study’s reliance on state-level data, as opposed to more localized data, might have affected the precision of the findings. The researchers acknowledge this and suggest that future studies could benefit from analyzing more fine-grained local data to better understand the dynamics at play.
“Currently, the only data available for this kind of US-wide multi-decadal analysis are at the level of US states, rather than, say, counties or zip-codes,” McCool said. “We expect that homicide rates are most strongly affected by local poverty and inequality, not so much what’s happening in a different city or on the other side of the state. As such, our analysis is necessarily somewhat coarse.”
“We hope that in the future higher resolution data will become available to track homicide rates in relation to very localized economic conditions. We should also note that the predictive power of our model was not uniform across US states, and underpredicted homicide rates in some instances. Nonetheless, the model did not underperform in any states for the 2020 COVID-19 data.”
Despite these limitations, the study offers crucial insights into the societal and policy implications of its findings. It underscores the need for interventions targeting both poverty reduction and the narrowing of income disparities to effectively tackle the root causes of increased homicide rates. Moreover, the study sheds light on the disproportionate impact of these socio-economic factors on minority communities, suggesting that addressing systemic racism and its contribution to economic disparities could be vital in reducing homicide rates.
“We contend that studies of homicide and, more broadly, human violence, should take heed of theoretical developments that provide explicit predictions of what conditions should promote violent behaviors, including homicide,” McCool told PsyPost. “By explicitly testing theory-based predictions we can work to avoid confusing causes with effects and move beyond the proverbial exercise of throwing spaghetti on the wall to see what sticks.”
The study, “U.S. homicide rates increase when resources are scarce and unequally distributed“, was authored by Weston C. McCool and Brian F. Codding.
