The impact of comorbidity of mental and physical conditions on role disability in the US adult household population

Context: There is limited information that accounts for comorbidity on the impact of role disability associated with a wide range of mental and physical disorders in population- based samples. Objective: To estimate the comparative effects of common mental and physical conditions on role disability in the general population using a novel method that accounts for comorbidity. Design: Direct interviews about physical and mental conditions during the past year. Setting: The National Comorbidity Survey Replication, a nationally representative series of face- to- face interviews. Patients: A nationally representative sample of adults living in households ( N= 5962 respondents, 18 years and older). Main Outcome Measure: Disability in major life roles was assessed with the World Health Organization Disability Assessment Schedule. Simulations that allow for complex interactions among conditions were used to estimate the conditions' effects on disability days, when respondents were completely unable to carry out their usual daily activities because of problems with mental or physical health, in the past 12 months. Results: An estimated 53.4% of US adults have 1 or more of the mental or physical conditions assessed in the survey. These respondents report an average 32.1 more roledisability days in the past year than demographically matched controls, equivalent to nearly 3.6 billion days of role disability in the population. Musculoskeletal disorders and major depression had the greatest effects on disability days. Mental conditions accounted for more than half as many disability days as all physical conditions at the population level. Associations of specific conditions with disability decreased substantially after controlling for comorbidity, suggesting that prior studies, which generally did not control for comorbidity, overestimated disea-sespecific effects. Conclusion: The staggering amount of health- related disability associated with mental and physical conditions should be considered in establishing priorities for the allocation of health care and research resources.