Original Articles

Mental–physical co-morbidity and its relationship with disability: results from the World Mental Health Surveys

K. M. Scott^a1 c1, M. Von Korff^a2, J. Alonso^a3, M. C. Angermeyer^a4, E. Bromet^a5, J. Fayyad^a6, G. de Girolamo^a7, K. Demyttenaere^a8, I. Gasquet^a9, O. Gureje^a10, J. M. Haro^a11, Y. He^a12, R. C. Kessler^a13, D. Levinson^a14, M. E. Medina Mora^a15, M. Oakley Browne^a16, J. Ormel^a17, J. Posada-Villa^a18, M. Watanabe^a19 and D. Williams^a20

^a1 Department of Psychological Medicine, Otago University, Wellington, New Zealand

^a2 Center for Health Studies, Group Health Cooperative of Puget Sound, Seattle, WA, USA

^a3 Health Services Research Unit, Institute of Municipal d'Investigacio Medica (IMIM), Barcelona, Spain

^a4 Department of Psychiatry, University of Leipzig, Germany

^a5 SUNY Stony Brook, Stony Brook, New York, USA

^a6 Institute for Development, Research, Advocacy and Applied Care (IDRAAC), Beirut, Lebanon

^a7 Department of Mental Health, AUSL di Bologna, Italy

^a8 Department of Neurosciences and Psychiatry, University Hospital, Gasthuisberg, Leuven, Belgium

^a9 Hôpitaux de Paris, Paris, France

^a10 Department of Psychiatry, University College Hospital, Ibadan, Nigeria

^a11 Sant Joan de Deu-SSM, Barcelona, Spain

^a12 Shanghai Mental Health Centre, Shanghai, People's Republic of China

^a13 Department of Health Care Policy, Harvard Medical School, Boston, MA, USA

^a14 Mental Health Services, Ministry of Health, Jerusalem, Israel

^a15 National Institute of Psychiatry, Mexico City, Mexico

^a16 Department of Rural and Indigenous Health, School of Rural Health, Monash University, Australia

^a17 Department of Psychiatry, University Medical Centre, Groningen, The Netherlands

^a18 Development Rehabilitation System FSC, Saldarriaga Concha Foundation, Bogota, Colombia

^a19 Department of Public Health, Jichi Medical University, Tochigi, Japan

^a20 Harvard School of Public Health, Boston, MA, USA

Abstract

Background The relationship between mental and physical disorders is well established, but there is less consensus as to the nature of their joint association with disability, in part because additive and interactive models of co-morbidity have not always been clearly differentiated in prior research.

Method Eighteen general population surveys were carried out among adults as part of the World Mental Health (WMH) Survey Initiative (n=42 697). DSM-IV disorders were assessed using face-to-face interviews with the Composite International Diagnostic Interview (CIDI 3.0). Chronic physical conditions (arthritis, heart disease, respiratory disease, chronic back/neck pain, chronic headache, and diabetes) were ascertained using a standard checklist. Severe disability was defined as on or above the 90th percentile of the WMH version of the World Health Organization Disability Assessment Schedule (WHODAS-II).

Results The odds of severe disability among those with both mental disorder and each of the physical conditions (with the exception of heart disease) were significantly greater than the sum of the odds of the single conditions. The evidence for synergy was model dependent: it was observed in the additive interaction models but not in models assessing multiplicative interactions. Mental disorders were more likely to be associated with severe disability than were the chronic physical conditions.

Conclusions This first cross-national study of the joint effect of mental and physical conditions on the probability of severe disability finds that co-morbidity exerts modest synergistic effects. Clinicians need to accord both mental and physical conditions equal priority, in order for co-morbidity to be adequately managed and disability reduced.

(Received May 15 2007)

(Revised January 21 2008)

(Accepted February 13 2008)

(Online publication March 26 2008)

Key Words:

• Co-morbidity;
• disability;
• interaction;
• mental;
• physical

Correspondence:

^c1 Address for correspondence: K. M. Scott, Ph.D., Department of Psychological Medicine, Otago University, Wellington, PO Box 7343 Wellington South, New Zealand. (Email: kate.scott@otago.ac.nz)