Violence against patients and staff on psychiatric wards is widely prevalent and increasing. While it is difficult to compare prevalence estimates among different studies, due to variations in definitions of violence, population studied, and the source of data collection, multiple studies from different countries have confirmed this to be the case (1,2). A study of 566 psychiatric and 898 nonpsychiatric beds from 16 psychiatric and general hospitals in the US reported 2.54 assaults per bed yearly among psychiatric wards, compared with 0.37 assaults per bed yearly in nonpsychiatric units (3). Similar estimates from other countries include the UK, with 0.65 attacks leading to property damage or injury to another person per occupied bed yearly (4); Belgium, with 1 aggressive incident per bed yearly (5); and Sweden, with 13 attacks per occupied bed yearly (6). Indeed, the experience of violence in the mental health system is so widespread that a multinational survey of psychiatric nursing staff across the US, Canada, the UK, and South Africa found that the respondents expected assaults in their work with psychiatric patients (7).

Various studies have also reported a significant increase with time in violent incidents. A British study that collected data over 15 months reported that the number of violent incidents in the second half of the study period constituted a highly significant 240% increase (P < 0.0001) over the number in the first half (8). Another British study reported a progressive increase in violence on an acute-care inpatient ward from 1976 to 1984 (9). Similarly, an American study reported a 32.9% increase in assault rates from 1978 to 1980 (10). Crowding appears to be emerging as one of many potential risk factors for this trend of wide prevalence and possible increase in violence on acute-care psychiatric wards. As psychiatric care continues to shift into the community, and as inpatient beds decrease, crowding will remain a major issue on acute-care wards (2,11–13). Two major outcomes of this trend can be identified: first, a group of patients with high readmission rates has emerged, resulting in a “revolving door syndrome.” Second, as noted, psychiatric inpatient units are getting crowded, with bed-occupancy rates often above 100% (13), which may be contributing to the trend (2,14,15).

Manuscript received November 2000, revised, and accepted April 2001.
¹Consultant Psychiatrist, Department of Psychiatry, Rotorua Hospital, Rotorua, New Zealand; Honorary Clinical Senior Lecturer, Division of Psychiatry, Auckland School of Medicine, Auckland, New Zealand.
²Psychiatric Registrar, Department of Psychiatry, Nepean Hospital, Sydney, New South Wales, Australia.
Address for correspondence: Dr S Kumar, Private bag 3023, Rotorua Hospital, Rotorua, New Zealand.
e-mail: kumars@lhl.co.nz

While crowding and violence on acute-care inpatient wards appear to be rising, studies of their relation have only begun to appear in the literature and often contradict each other. A few studies have reported no association between crowding and aggression (16–18), but others have reported that increased inpatient numbers lead to more aggression by patients against both staff and other patients (6,19,20). Indeed, in a 12-month retrospective study of our own unit, increased ward occupancy was found to be associated with both physical and verbal aggressive incidents (21).

There has been little written on why psychiatric patients should respond to crowding with violence and what, if any, are the possible solutions. This paper examines the relation with a view to developing explanatory models for it. To this effect, we review the literature from 6 different areas that explain a rise in stress levels in crowded situations. We propose that high stress level on a crowded ward acts as a precipitating factor for violence through at least 2 mechanisms: First, on a crowded ward, patients’ appraisal of their environment may easily become distorted, leading to misinterpretation of ward activities and culminating in assaults (22). Second, it is a well-known fact that when stress level crosses a certain threshold our tolerance level decreases, leading to a reduced ability to cope that may, in turn, lead people to lose control and assault others. The contributions from the 6 reviewed areas are united in the context of acute-care psychiatric wards. Finally, we suggest some strategies to counter the effects of crowding and make recommendations for future studies. For this review, we defined violence as any unwelcome physical or sexual contact or threat to kill or harm with a weapon. We did not include simple verbal threats or damage to property. We acknowledge that such incidents may be distressing to the victims or to people witnessing the incident, but we believe that their impact is less severe.

Area 1: Density, Privacy, and Control

Density, privacy, and control are 3 interrelated variables described in the psychological literature that may help in understanding the relation between crowding and violence. These variables are generally used when investigating the impact of architecture on human mood and behaviour (23). “Density” has been defined as the number of individuals per unit of space (24). One review has identified 2 types of density in relation to crowding and violence on psychiatric wards: “social density,” or number of people in a given area, and “spatial density,” or size of an area used by a given number of individuals (14). With an increase in social density, stress increases, and an individual’s privacy and control, actual and perceived, decrease (23).