Hospitalisations due to interpersonal violence: a population-based study in Western Australia

Interpersonal violence is a significant public health issue in terms of its impact on the community and the health care system, both at a national and international level. Globally, interpersonal violence accounts for 10% of all deaths, which translates to half a million deaths a year.1 About 11% of these deaths occur in the Western Pacific Region (as defined by the World Health Organization).2 In Australia, interpersonal violence accounts for 4% of all injury deaths and ranks fifth as a primary reason for death from all other causes.3,4 In Western Australia, for each year of the period 1989–2000, an estimated 70 000 people were assaulted, about 3000 people were hospitalised as a result of assault or maltreatment, and 30 people were murdered.5-7 In terms of cost to the community, it was conservatively estimated that a third of the cost of injury in 2003 in WA could be attributed to interpersonal violence.8

Interpersonal violence is one of three categories of violence that have been identified by the WHO. The other two categories are self-directed violence (suicide) and collective violence (war). The WHO defines interpersonal violence as:

This definition includes victimisation perpetrated against intimate partners, parents, siblings, children, other relatives, friends, aquaintances, colleagues and strangers. There are many documented risk factors for interpersonal violence, including gender, age, poverty, alcohol and/or substance misuse disorders, a history of violent behaviour, Indigenous status and mental illness.9-12 Previous research has also reported increased use of health services by victims of violence.13 However, there has been little research into which groups are at particularly high risk of being involved in a subsequent incident of interpersonal violence, and, given the high cost to the health care system of such cases, preventive action is needed.

Although there has been a move towards preventive approaches, a lack of data at the population level has made it difficult to develop appropriate, evidence-based initiatives. Different definitions of interpersonal violence, small sample sizes, and lack of adjustment for confounders have been the major limitations to previous observational studies.10-13

The aims of our study were to quantify the impact on the WA health care system of hospitalisations due to interpersonal violence and to identify risk factors for repeat hospital admissions for interpersonal violence.

We conducted a population-based, retrospective study of all hospital admissions of people of all ages due to interpersonal violence in WA over the period 1990–2004 using linked data from the WA Mortality Database, the Hospital Morbidity Data System (HMDS) and the Mental Health Information System (MHIS).

The Data Linkage Unit at the WA Department of Health retrieved de-identified data for the period 1990–2004. Hospital records in which the primary diagnosis was “injury” and the external cause was “injury inflicted by another” were extracted from the HMDS for the study period. This dataset was externally linked to the WA Mortality Database to identify deaths and the MHIS to identify all mental health service contacts from 1966 onwards. In view of the long-term nature of mental illness, the longer time frame for the MHIS was necessary to ensure that misclassification did not occur.

Our results highlight the burden on the health care system resulting from multiple hospital admissions for interpersonal violence.

Indigenous victims of interpersonal violence accounted for nearly half of all hospitalisations, despite representing only 3%–4% of the WA population. The high rate of hospitalisations among Indigenous people in WA is comparable with data recorded for other states.18,19

Our finding that people with a mental illness were significantly more likely to be re-admitted than those without is consistent with previous reports of a positive association between mental illness and the risk of violence.20-22 Women and Indigenous people were also at an increased risk for a second hospital admission for interpersonal violence. In developing a response to violence and its associated problems (such as psychological harm), a variety of agencies and sectors of the community should be involved in prevention activities, and programs should be tailored to suit different cultural settings and population subgroups. Evaluation should be an integral part of any intervention program, so that lessons can be learnt and shared regarding what may and may not help to prevent violence.

Additionally, living in rural or remote areas posed significant risk for a repeat hospital admission for interpersonal violence. This is an important finding because, to be effective, services and preventive efforts must be appropriately focused on groups and areas identified as being at high risk.

The presence of comorbidities increased the risk of a repeat hospital admission due to interpersonal violence. Indeed, recent research shows that interpersonal violence has wide ranging consequences for the victim’s physical and mental health that may transcend the specific effects of the violent event itself.9,23,24

Low socioeconomic status, in particular the extremely disadvantaged group, was likely to be associated with a repeat episode of violence. The result lends support to the literature showing that interpersonal violence rises as area-level disadvantage increases.13

A limitation of our study was that the HMDS captured only victims that sought treatment at a hospital. It is well known that many violent events in domestic situations are never reported.25,26 Therefore, the hospitalisation cases studied are likely to be those at the moderate-to-severe end of the injury spectrum. Nevertheless, hospital records can serve as good indicators of interpersonal violence at the community level as far as serious injury is concerned.

Another limitation was the lack of lifestyle information such as smoking status, alcohol and drug usage, and living conditions. Socioeconomic status categories, which were based on residential postcodes, may not have been accurate. Moreover, the presence of comorbidities referred to other conditions recorded at the first hospital admission.

Despite these limitations, we believe the results of our study will help researchers to plan and implement future interventions to reduce interpersonal violence in WA.

In conclusion, priority should be directed towards the primary prevention of violence. This will ultimately reduce hospitalisations due to interpersonal violence. High-risk groups such as women, Indigenous people and those with a mental illness should be targeted for special attention.