By: Joshua C. Hinkle, David Weisburd, Christine Famega, and Justin Ready

Background: Hot spots policing is one of the most influential police innovations, with a strong body of experimental research showing it to be effective in reducing crime and disorder. However, most studies have been conducted in major cities, and we thus know little about whether it is effective in smaller cities that account for a majority of police agencies. The lack of experimental studies in smaller cities is likely partly due to challenges of designing statistically powerful tests in such contexts.

Objectives: The current paper explores the challenges of statistical power and “noise” resulting from low base rates of crime in smaller cities and provides suggestions for future evaluations to overcome these limitations.

Research Design: Crime data from a randomized, experimental evaluation of broken windows policing in hot spots are used to illustrate the challenges that low base rates present for evaluating hot spots police innovations in smaller cities.

Results: Analyses show that low base rates make it difficult to detect treatment effects. Very large effect sizes would be required to reach sufficient power, and random fluctuations around low base rates make detecting treatment effects difficult irrespective of power by masking differences between treatment and control groups.

Conclusions: Low base rates present strong challenges to researchers attempting to evaluate hot spots policing in smaller cities. As such, base rates must be taken directly into account when designing experimental evaluations. The paper offers suggestions to researchers who attempt to expand the examination of hot spots policing and other microplace-based interventions to smaller jurisdictions.