Philadelphia Hot Spots Policing
Philadelphia Police Department / Lawrence Sherman / Jerry Ratcliffe · Philadelphia, USA · 1995
Summary
Rather than spreading patrol thinly across precincts, hot spots policing concentrates resources at the tiny fraction of locations responsible for the majority of crime. Sherman and Weisburd's Philadelphia experiment—later extended by Ratcliffe and colleagues—found that concentrating patrol at high-crime micro-locations reduced crime significantly and, critically, did not push crime into adjacent streets. In fact, crime fell in nearby areas too (diffusion of benefits). The study is the foundation of evidence-based policing and one of the most replicated criminology experiments.
Research question
"Does concentrating police patrol at high-crime 'hot spots' (micro-locations) reduce crime, and does crime displace to adjacent areas?"
Methodology
Intervention
Doubled police patrol time at randomly selected high-crime street segments and intersections (hot spots)
Assignment
Randomized controlled trial (street segment/intersection)
Sample size
110 matched pairs of hot spots
Primary outcome
Calls for service; observed criminal incidents; displacement to adjacent areas
Effect estimate
−15% crime incidents at treated hot spots; no evidence of displacement to adjacent areas; 'diffusion of benefits' observed (crime fell in areas immediately adjacent to treated spots)
Decision
Hot spots policing adopted by major police departments worldwide; replicated in 19+ studies; became dominant evidence-based policing strategy
Result
Positive
−15% crime incidents at treated hot spots; no evidence of displacement to adjacent areas; 'diffusion of benefits' observed (crime fell in areas immediately adjacent to treated spots)
Evidence strength
Strong
Randomized trial, replicated across multiple sites or studies.
Replication status
Replicated
Institution
Philadelphia Police Department / Lawrence Sherman / Jerry Ratcliffe
Location
Philadelphia, USA
Year
1995
Policy area
Public Safety
Mechanism
Targeting