The Association Between Vacant Lot Redevelopment and Violent/Firearm Violent Crime: A Difference-in-Difference Analysis From 2007 to 2023

<b>Objectives.</b> To investigate the association between vacant lot redevelopment and violent crime and firearm violent crime. <b>Methods.</b> We used a quasi-experimental study with a difference-in-difference (DID) design. The study population was 254 vacant lots located in Philadelphia, Pennsylvania. The exposure was redevelopment, defined as repurposing the vacant lot into a permanent structure (e.g., housing) between 2007 and 2023. The outcome was violent crime subtypes and firearm violent crime subtypes reported to the police. Our primary analysis used a staggered DID estimator. <b>Results.</b> We found a negative association between redevelopment and aggravated assault (DID = -56.55 crimes per square mile per year; 95% confidence interval [CI] = -97.86, -15.24), firearm aggravated assault (DID = -35.11 crimes per square mile per year; 95% CI = -55.41, -14.82), and overall firearm violent crime (DID = -27.26 crimes per square mile per year; 95% CI = -52.97, -1.54). We did not find significant associations for the other outcomes tested. <b>Conclusions.</b> Our results support the hypothesis that vacant lot redevelopment may prevent or displace violent crime. <b>Public Health Implications.</b> Built environment investments may prevent or displace violence. (<i>Am J Public Health</i>. 2026;116(1):95-102. https://doi.org/10.2105/AJPH.2025.308269).