The Mass Murder as Quasi-Experiment: The Impact of the 1996 Port Arthur Massacre

Few crimes command as much attention as mass murder. Depending on their magnitude and context, some of these incidents become enshrined as landmark historical events. Some give rise to substantial policy change. One such event in Australia was the Port Arthur Massacre that claimed 35 lives in 1996. Using a disaggregation strategy and intervention analysis, this article explores the impact of the Port Arthur massacre on subsequent homicides in Australia. The results of the analysis indicate that the Port Arthur incident appears to have had no lasting effect on homicide in Australia. However, there was an immediate increase in firearm homicides during the 5 days following the massacre. After this sudden increase, the incidence of homicide resumed its long-term downward trend. This sudden increase can be interpreted as evidence of a contagion effect, with the significant response by the Australian Government contributing to the incidence of homicide resuming its long-term trend, rather than continuing to increase.