Adversary effects and the tactics of violent offenders.

We examine the implication of adversary effects for target choice, lethal intent, and the use of weapons and allies in violent incidents. Adversary effects refer to the tendency of offenders to make tactical decisions based on the coercive power of victims and potential victims. Using the victim's gender as a proxy for coercive power, we analyzed violent incidents from the National Incident-Based Reporting System (2005-2014). The sample included over six million assaults, robberies, and homicides. Consistent with adversary effects, offenders who attack males (vs. females) are more likely to (a) kill victims; (b) use guns, knives, blunt objects, poison, and automobiles; (c) use male (but not female) allies; and (d) use multiple allies. The evidence for target choice is mixed: unarmed female offenders, but not unarmed male offenders, are more likely to target females than males. The evidence shows how a simple theoretical principle can parsimoniously account for basic patterns of violence in society related to gender, weapons, and group violence.