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Journal of Public Health Advance Access published online on August 18, 2008
Journal of Public Health, doi:10.1093/pubmed/fdn069
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© The Author 2008, Published by Oxford University Press on behalf of Faculty of Public Health. All rights reserved

Effects of demographic variables on mental illness admission for victims of interpersonal violence


Lynn Meuleners, Senior Research Fellow
Andy H. Lee, Professor of Biostatistics
Delia Hendrie, Lecturer in Public Health

School of Public Health, Curtin University of Technology, GPO Box U 1987, Perth, WA 6845, Australia


Address correspondence to Andy H. Lee, E-mail: andy.lee{at}curtin.edu.au

Background To assess the effects of demographic factors on mental illness admission for victims of interpersonal violence.

Methods A population-based retrospective cohort study was conducted to investigate victims of violence using the 1990–2004 linked data extracted from the Western Australia Hospital Morbidity Data System and the Mental Health Information System. Factors associated with the risk for hospitalization for mental illness were assessed by logistic regression analysis.

Results Among the 25 427 victims admitted to hospital for at least one episode of interpersonal violence during the study period, 6395 (25%) had been hospitalized with a mental illness diagnosis. Female [odds ratio (OR) 1.54, 95% CI 1.40–1.63] and Indigenous (OR 1.47, 95% CI 1.34–1.57) victims of violence were significantly more likely to be admitted for mental illness. The presence of additional co-morbidity also increased the risk (OR 1.49, 95% CI 1.44–1.54). Other variables that significantly increased the risk of mental illness admission were advancing age, other methods of assault and victims who had been separated, divorced or widowed.

Conclusions The results are beneficial for designing and implementing intervention strategies to reduce the adverse consequences of interpersonal violence particularly for women and Indigenous victims of violence.

Keywords: hospital admission, interpersonal violence, mental illness, risk factors


   Introduction
TOP
 Introduction
Methods
 Results
 Discussion
 Conclusion
 Funding
 Acknowledgements
 References
 
Improving mental health diagnoses, screening and treatment and preventing injuries are public health priorities.1 Categorized as a significant injury condition, interpersonal violence accounts for ~4% of all injury deaths in Australia and is one of the leading contributors of cost to the health-care system.2 Mental illness is a major cause of disease burden in Australia, exceeded only by cardiovascular disease and cancer. Within the State of Western Australia (WA), nearly one in five individuals suffer from a diagnosable mental disorder which includes chronic depression, anxiety disorders and schizophrenia.3,4

According to the World Health Organization, interpersonal violence is one of the three categories of violence, the other two categories being self-directed violence (i.e. suicide) and collective violence (i.e. war).5 Psychological harm is also identified as an outcome of interpersonal violence.5 Past research has shown that mental illness is prevalent among this particular group of individuals, especially those who have a history of alcohol and substance misuse, self-harm and suicide, depression, phobias, schizophrenia, anxiety disorders and post-traumatic stress disorder.6–9

Epidemiological studies have established a link between mental disorders and violence.10–12 Community surveys as well as case studies suggested that victims are at increased risk of psychiatric symptoms and long-term psychiatric disorders. In addition, studies of clinical populations have reported high rates of lifetime victimization among psychiatric patients.13–15 However, the majority of these studies were cross-sectional surveys of people with mental illness. The samples consisted mostly of individuals receiving treatment for moderate to severe cases of a specific psychiatric disorder, predominantly schizophrenia, making it difficult to generalize their findings to other diagnosed groups (e.g. depression) and population (e.g. non-treated).16 Moreover, these studies adopted a variety of definitions of interpersonal violence, ranging from perceived threat of assault to actual assault with varying degrees of injury severity.17,18 They also measured violence victimization generally by self-report, thus liable to both under- and over-reporting.

In WA, a population-based approach was used to compare the health status of people with and without a mental illness. Those with a mental illness were found to have a higher risk for all types of injuries, particularly drug-related poisoning and injuries inflicted by others.19 Recently, a WA population-based study showed that mental illness patients were about 1.5 times more likely to incur repeat hospital admissions for interpersonal violence.20 To further investigate the relationship between interpersonal violence victimization and mental illness, the present population-based study examined risk factors for hospitalization due to mental illness among victims of violence using linked hospital morbidity and mental health administrative data. The findings would be important for the development of public health interventions to reduce the adverse health consequences of violent victimization.


   Methods
TOP
 Introduction
 Methods
Results
 Discussion
 Conclusion
 Funding
 Acknowledgements
 References
 
Study design
A population-based, retrospective cohort study of all hospital admissions in WA due to interpersonal violence and mental illness was undertaken using linked administrative data from 1990 to 2004. The de-identified data set was obtained from the Data Linkage Unit at the Department of Health, WA. The Hospital Morbidity Data System (HMDS) constitutes the largest component of the WA Linked Database, and contains over 7 million records of inpatient episodes for all acute hospital admissions to public and private hospitals in the State. The Mental Health Information System (MHIS) contains data in excess of 200 000 patients of mental health services for the population of WA. Each individual patient record has been linked by means of probabilistic matching. Name, residential address, date of birth and sex are the principal fields used in the probabilistic matching. The WA Linked Database is a dynamic system, which is constantly being revised and updated as new data become available and are added to the system.

Hospitalization records, in which the primary diagnosis was an ‘injury’ and the external cause was ‘injury inflicted by another’, were extracted from the HMDS for the study period. This data set was externally linked to the MHIS to identify all mental health service contacts from 1966 onwards. In view of the long-term chronic nature of mental illness, the extended time frame for MHIS data extraction was necessary to ensure that misclassification of cases did not occur. Ethics approval was obtained from the Human Research Ethics Committee of Curtin University of Technology and the Confidentiality of Health Information Committee of WA.

Operational definitions
Interpersonal violence
The term ‘interpersonal violence’ was defined as ‘physical injury inflicted by other persons, severe enough to require hospitalization, resulting from violence between intimate partners, family or community members (including child and elder abuse, domestic and youth violence, random acts, rape and sexual assault by strangers and violence in institutions such as schools)’.21–23

Mental illness
‘Mental illness’ was a diagnosable disorder that significantly interfered with an individual's cognitive, emotional or social abilities and differs from ‘mental health problems’ only in duration and severity.22

Victim of violence admitted to hospital
A case was defined as a ‘victim of violence’ if the principal diagnosis for at least one hospital separation in the case's record was an ‘injury’ as designated by a diagnosis code between 800.00 and 999.99 (Chapter 17, ICD-9-CM),24 or between S00.0 and T98.3 (Chapter XIX, ICD-10-AM),25 and a primary external cause indicating that at least one injury in the case record was inflicted by another person, as designated by an external cause code between E960.0 and E969 (ICD-9-CM),24 or between X85 and Y09 (ICD-10-AM).25

Victim of violence with mental illness admitted to hospital
A case was defined as a ‘victim of violence with a mental illness’ if the case met the criteria for ‘victim of violence’ above and the case's record included at least one hospital separation for which any diagnosis is a mental or behavioural disorder, as designated by a diagnosis code between 290 and 319 (Chapter V, ICD-9-AM)24 or F00 and F99 (Chapter V, ICD-10-AM).25

Co-morbidity
This was defined as the presence of one or more specific health conditions, which were defined using the broad ICD-9-CM and ICD-10-AM chapter headings unless the condition was an injury at the time of the admission for interpersonal violence.

Type of assault
This was defined using subgroupings in the major injury grouping framework devised by the Centers for Disease Control and Prevention. The external cause codes for injury inflicted by another were divided into four subgroups designating the following methods of inflicting injury: ‘by bodily force’ [E960.0 (ICD-9-CM) or Y04 (ICD-10-AM)], ‘by sharp or blunt object’ [E966, E968.2 (ICD-9-CM) or Y99, Y00 (ICD-10-AM)], ‘by maltreatment or rape’ (E960.1, E967.0-9 (ICD-9-CM) or Y05, Y06.0-9, Y07.0-9 (ICD-10-AM)) and ‘by other methods’ [all other codes between E960.0 and E969 (ICD-9-CM) or X85 and Y09 (ICD-10-AM)].

Statistical analysis
Victims who had been admitted more than once during the study period were flagged but were considered only once at the individual patient level. Information at the index admission for interpersonal violence was used in the statistical analyses. Any subsequent admissions generated by patient transfer between hospitals (<28 days) were combined with the initial hospitalization into one inpatient episode.

Descriptive statistics were used to contrast the profile of victims of interpersonal violence with and without a hospitalization for mental illness. Logistic regression analysis was then undertaken to identify factors affecting mental illness admission for all victims of interpersonal violence who had been admitted to hospital during the study period. The available factors extracted from the database were age, gender, residential location, Indigenous status (Indigenous, non-Indigenous), marital status (not married, married, separated/divorced/widowed), type of assault and number of co-morbidities (ranging from 0 to 7). Residential location was categorized as metropolitan, rural or remote using the WA's Hospital Department zones classification.


   Results
TOP
 Introduction
 Methods
 Results
Discussion
 Conclusion
 Funding
 Acknowledgements
 References
 
A total of 25 427 victims were admitted to hospital for at least one episode of interpersonal violence during the study period. Among them, 5848 (23%) of them had two or more episodes of interpersonal violence whereas 6395 (25%) had been hospitalized with a mental illness diagnosis. Of these mental illness admissions, 3534 cases (55%) were incurred prior to their first interpersonal violence episode, whereas 2861 victims (45%) were admitted for mental illness after their hospitalization for violence.

Table 1 compares the characteristics of victims with and without a mental illness admission. Victims with a mental illness admission (mean age 32 years) were slightly older than those without (28 years). The proportion of women was higher among the mental illness group (37% versus 26%), whereas Indigenous people accounted for 42% of the victims hospitalized for mental illness, compared with the 31% Indigenous victims without a mental illness admission. Differences in distributions between the two groups were also found with respect to marital status, residential location and type of assault. The mean number of co-morbidities was significantly higher among those with a mental illness admission (0.86, SD 1.07) than those without (0.47, SD 0.80).


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  		Table 1 Characteristics of victims of interpersonal violence with and without a mental illness hospital admission in Western Australia, 1990–2004

 
Results of the logistic regression analysis are presented in Table 2. Female [odds ratio (OR) 1.54, 95% CI 1.40–1.63] and Indigenous (OR 1.47, 95% CI 1.34–1.57) victims of violence were significantly more likely to be admitted for mental illness. The presence of additional co-morbidity also increased the hospitalization risk by 1.5-fold (OR 1.49, 95% CI 1.44–1.54). Victims of violence residing in remote areas were less likely to incur a mental illness admission than their metropolitan counterparts (OR 0.85, 95% CI 0.78–0.93). Other variables that significantly increased the risk of mental illness admission were advancing age, other methods of assault and victims who had been separated, divorced or widowed.


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  		Table 2 Factors affecting mental illness admission for victims of interpersonal violence (n = 22 471)

 
To further examine whether the temporal sequence of events could make an impact, separate analyses were undertaken for (i) victims who incurred their mental illness admission before the first violent episode and (ii) those victims admitted for mental illness after their violent hospitalization. The adjusted OR and associated 95% confidence intervals for Group (i) were similar to those of all victims above, although the type of assault was no longer significant. For Group (ii), results were again comparable, except that advancing age (OR 1.01, 95% CI 1.00–1.01) and victims who had been separated, divorced or widowed (OR 0.99, 95% CI 0.81–1.21) did not significantly affect the risk of mental illness admission, with P-values of 0.15 and 0.94, respectively.


   Discussion
TOP
 Introduction
 Methods
 Results
 Discussion
Conclusion
 Funding
 Acknowledgements
 References
 
Main finding of this study
The results provide further evidence of the association between mental illness and violence.10–12 One in four individuals who were involved in a violent incident was admitted at least once to hospital with a diagnosis of a mental illness. Female and Indigenous victims of violence were significantly more likely to be admitted for mental illness. The presence of additional co-morbidity also increased the risk of mental illness admission. Living in remote areas of the State appeared to have a lower risk of mental illness hospitalization compared with metropolitan areas. However, the decreased risk may be due to the limited access to health-care services in remote areas.26

What is already known on this topic
There is no simple cause-and-effect relationship between violence and its impact, particularly where psychological harm is concerned. It has been suggested that mental illness may be exacerbated as well as contribute to interpersonal violence.27 Analysing the temporal sequence of events between mental illness and interpersonal violence and examining the specific psychiatric condition that could manifest as a result of victimization would help to understand the relationship. The linked data provide an opportunity to investigate the psychological harm outcomes that might arise or precipitate from each type of assault or maltreatment. In WA, a population-based study using linked data has found that mental illness patients had a significantly higher risk of being readmitted for interpersonal violence.20

What this study adds
This study demonstrated the increased risk of mental illness for female victims of violence. Previous research has also found that women exposed to violence are at a greater risk for both mental and physical health problems.28 Physical health problems can include stress, permanent disabilities, cardiac symptoms, seizures and reproductive problems.29–31 Mental health problems can include long-term anxiety and depression, alcohol and substance abuse.32

In Australia, Indigenous violence is highly prevalent and disproportionately high when compared with the general population.33 Although Indigenous people represent only 3–4% of the population in WA, their risk for a mental illness admission among victims of violence was almost 50% greater than their non-Indigenous counterparts. Factors such as being disadvantaged economically, loss of culture, broken family ties and alcohol and/or substance abuse have been found to contribute to the risk of experiencing interpersonal violence in Indigenous communities.34,35

This study has highlighted the effect of co-morbidities for victims of violence. It has been reported that women with co-morbidities, in particular mental health problems, were at increased risk for involvement in interpersonal violence.13,27 Strengthening general practice care for people with a mental illness would be one way of improving their health outcomes. If an individual's condition could be better managed and a coordinated approach to total health adopted, the risk of being admitted to hospital may be reduced.

Limitations of this study
There are several limitations when using linked data. In this study, the databases covered only those who sought treatment at a hospital. It is known that many events, especially those in domestic situations, are never reported.28 Additionally, the MHIS does not capture all patients with a mental illness. At any one time ~8% of the WA population is recorded on the MHIS.19 However, the 1997 Survey of Mental Health and Well-Being found that almost 20% of the population had a diagnosable mental illness. Many victims of violence with a mental illness do not seek treatment, whereas some may be treated by general practitioners or private psychiatrists on an outpatient basis. These patients probably have less severe injuries as a result of interpersonal violence or less severe forms of mental illness, consequently not being captured in the system. Therefore, the cases studied are likely to represent those at the moderate to severe end of the illness spectrum. Another limitation is the lack of information on lifestyle factors such as smoking, alcohol consumption, drug usage, living conditions and socio-economic status, which can influence the hospitalization risk. Finally, the mentally ill are more prone to being victimized by people whom they share a close relationship.32 However, this study was unable to determine the relationship between victim and perpetrator, particularly for those with a mental illness. The Department of Health is now collecting data related to this issue and further research is warranted.


   Conclusion
TOP
 Introduction
 Methods
 Results
 Discussion
 Conclusion
Funding
 Acknowledgements
 References
 
This study has further demonstrated the link between psychological harm and interpersonal violence at the population level. The findings are useful for the design and implementation of intervention strategies to reduce the adverse consequences of interpersonal violence. The development of intervention for individuals with a mental illness requires detailed examination of the characteristics of their victimization14 so that further research to identify the underlying causes of violence is needed. The evidence from this study suggests that preventive programs should be tailored to suit different cultural settings and population subgroups, with female and Indigenous victims of violence targeted for special attention.


   Funding
TOP
 Introduction
 Methods
 Results
 Discussion
 Conclusion
 Funding
Acknowledgements
 References
 
The research was supported by a grant (35/05-06) from the Criminology Research Council of Australia.


   Acknowledgements
TOP
 Introduction
 Methods
 Results
 Discussion
 Conclusion
 Funding
 Acknowledgements
References
 
The authors would like to thank Chris Gillam for her assistance with the project and the Data Linkage Unit at the Department of Health, Western Australia, for data extraction. There is no competing interest declared for all authors.


   References
TOP
 Introduction
 Methods
 Results
 Discussion
 Conclusion
 Funding
 Acknowledgements
 References
 

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