To what extent is intoxication associated with aggression in bars? A multilevel analysis.

Objective: The purpose of this study was to assess the relationship between level of intoxication and the frequency and severity of aggression at the person, incident, visit, and bar level for aggressive incidents observed in bars or clubs.

Method: Hierarchical Linear Modeling (HLM) analysis of 1025 incidents of aggression documented by trained observers during 1334 nights of observation in 118 bars and clubs in Toronto, Canada, was conducted.

Results: Both level of intoxication of the crowd during the visit as well as mean level of intoxication at the bar level significantly predicted frequency of aggression. There was a positive association between level of intoxication and severity of aggression at both the incident and person level except for the highest level of intoxication at the person level, where severity of aggression was less than for moderate intoxication. A person-incident level interaction between intoxication and severity of aggression was also found.

Conclusions: These results suggest that prevention efforts should focus on both identifying bars that typically have more intoxicated patrons and reducing the intoxication levels of patrons across bars generally. The results also showed a strong positive relationship between level of intoxication and severity of aggression (except at the highest levels), indicating that intoxication increases risk in terms of both frequency and severity of aggression. The significant interaction between person- and visit-level intoxication suggests that greater attention needs to be paid to group dynamics in alcohol-related aggression.