The Impact of the First Professional Police Forces on Crime

This paper evaluates how the introduction of professional police forces affected crime using two natural experiments in history: the 1829 formation of the London Metropolitan Police (the first police force ever tasked with deterring crime) and the 1839 to 1856 county roll-out of forces in England and Wales. The London Met analysis relies on two complementary data sources. The first, trial data with geocoded crime locations, allows for a difference-indifferences estimation that finds a significant and persistent reduction in robbery but not homicide or burglary. A pre-post analysis of the second source, daily police reports of both cleared and uncleared crime incidents, finds a significant reduction in all violent crimes but offsetting changes in uncleared (decrease) and cleared (increase) property crimes. These (local) reductions in crime are not just due to crime displacement but represent true decreases in overall crime. Difference-in-difference analyses of the county roll-out find that only sufficiently large forces, measured by the population to force ratio, significantly reduced crime. The results are robust to controlling for spill-over effects of neighboring forces.