Violence in psychiatric wards is common, and it is on the rise. This study examined the frequency and types of aggressive and violent behaviors in acute psychiatric inpatient settings and focuses on the possible complex interaction between ward staffing, patient mix, and violence.

Data were gathered prospectively in two acute psychiatric units in two general hospitals and two units in a psychiatric hospital in Isfahan, Iran. Staff recorded violent and aggressive incidents by using Morrison's hierarchy of aggressive and violent behavior. They also completed weekly reports of Ward Activity Index (patient mix), and Staff Level Index were developed by the researcher. Regression analysis was used to calculate relative rates.

A total of 429 violent incidents were recorded over a three-month period. Based on the scale, more than 50 percent of the incidents were serious. Seventy-eight percent were directed toward nursing staff. Complex relationships between staffing, patient mix, and violence were found. Relative risk increased with more nursing staff (of either sex), more non nursing staff on planned leave, more patients known to instigate violence, a greater number of disoriented patients, more patients detained compulsorily, and more use of seclusion. the relative risk decreased with more young staff (under 30 years old), more nursing staff with unplanned absenteeism, more admissions, and more patients with substance abuse or physical illness.

Violent incidents within psychiatric facilities were frequent and serious, with great significance for occupational health. Some clues were found in the prediction of violence.