Health burden in chronic disease: multimorbidity is associated with self-rated health more than medical comorbidity alone.

OBJECTIVES To investigate the association between multimorbidity-a construct comprising several health domains (medical comorbidity, musculoskeletal, physical and social functional status, mental health, and geriatric problems)-and overall self-rated health (SRH), an important chronic disease health outcome. We investigate whether medical comorbidity effects are mediated through other health domains and whether these domains have independent effects on SRH. STUDY DESIGN AND SETTING Medicare recipients (n=958) completed a questionnaire 3 years post primary total hip replacement surgery. Self-reported sociodemographic characteristics, SRH, and health domain statuses were ascertained. Probit regressions and path analyses were used to evaluate the independent effects of the health domains on SRH and the interrelationships between domains and to quantify direct and mediated effects. RESULTS All domains were independently associated with SRH. Medical comorbidity explained 11.7% of the variance in SRH, and all other health domains explained 27.3%. The impact of medical comorbidity was largely direct (only 21.5% mediated through other domains). Medical comorbidity minimally explained the variance in other domain scores. CONCLUSION SRH has multiple determinants. This finding suggests that an exclusive focus on any one domain in health research may limit the researchers' ability to understand health outcomes for which SRH is predictive.