Violence in psychiatric wards is common, and it is on the rise. This study examined the relationship between ward occupancy level and staff-to-patient ratio and incidents of aggressive behavior, both physical and verbal, on an acute inpatient unit in Iran.

Logistic regression was used to analyze data collected from the ward's log of adverse incidents and the ward census over a 12-month period. A physical incident was defined as an unwelcome physical contact or willful damage to property. Incidents of self-harm were excluded. Verbal aggression was any threat of physical or sexual harm.

Among 381 admissions during the study period, 58 incidents were recorded--25 incidents of verbal aggression and 33 incidents of physical violence. Logistic regression demonstrated that the occupancy level was positively associated with the occurrence of any type of violent incident. The average occupancy level when an incident occurred was 77 percent, compared with 69 percent when no incidents occurred. The average occupancy level was significantly higher when verbal incidents occurred (80 percent) than when physical incidents occurred (70 percent). No association was found between violence and staff-to-patient ratio. Incidents were significantly more likely to occur during the afternoon shifts (3 p.m. to 11 p.m.).

Crowding was found to be significantly associated with aggressive incidents, and in particular with verbal aggression.