• Reactivity;
  • police observational data;
  • decision to arrest;
  • observer sex;
  • acclimation effects

Data from a large-scale observational study of police examined the impact of an observer's presence on patrol officer arrest behavior. One major theme within the descriptive data on reactivity (concerns about safety) was described as a series of anecdotes and specified in terms of its prevalence. Consistent with hypothesized effects, patrol officers who expressed concerns about safety were less likely to arrest suspects. Additional analyses also revealed that patrol officers were less likely to arrest when accompanied by female versus male observers and that there is a different pattern of acclimation that is contingent on a combination of observer sex and concerns about safety. The implications of these findings and suggestions for future research will also be considered.