Methods/Statistics
Beyond per-capita rates: Urban scaling of female firearm homicides in the United States Roni Barak Ventura* Roni Barak Ventura Barak Ventura New Jersey Institute of Technology
Epidemiologic rates are typically standardized by population size, however, growing evidence suggests that rural and urban systems differ in more fundamental ways that are not fully captured by per-capita measures. Urban Scaling Theory models cities as complex systems analogous
to biological organisms, whose behaviors are better described by scaling laws such as Kleiber’s Law and Ideal Gas Law. Empirical studies show that urban infrastructure (e.g., roads, cables, and built area) scales sublinearly with population size, whereas socioeconomic phenomena (e.g., GDP, patents, and social interactions) scale superlinearly. By explicitly accounting for population-dependent nonlinearities, urban scaling enables more equitable comparisons across spatial units of different sizes.
Urban scaling provides an appropriate framework for modeling epidemiologic variables such as event incidence, risk factors, and the distribution of resources to mitigate them across the urab-rural continuum. We demonstrate the utility of this approach by examining the distribution of female firearm homicides across U.S. cities. We analyzed data from 917 U.S. cities for three periods: pre-pandemic (2018–2019), during the pandemic (2020–2021), and post-pandemic (2022–2023). For each period, we fit a power-law model relating homicide counts to city population size and recorded the corresponding scaling exponent β. Female firearm homicides exhibited strictly sublinear scaling across all periods, indicating a disproportionate burden in less populous, more rural areas. However, the scaling exponent increased significantly during the pandemic (β = 0.711 ∈ [0.668, 0.754] in 2018-2019 and β = 0.804 ∈ [0.761, 0.846] in 2020-2021) and following the pandemic (β = 0.903 ∈ [0.872, 0.933] in 2022-2023). This finding suggests a growing incidence of these homicides in more densely populated cities. These results align with reports of increased domestic violence and femicide during and following the COVID-19 pandemic.