This study provides nationally-representative data quantifying the prevalence and characteristics of role impairment associated with a wide range of mental and chronic medical disorders. Three main findings build on and extend previous data on the relative burden of mental and chronic medical disorders in the United States. First, the findings document that the mental disorders considered here are significantly more impairing than the commonly occurring chronic medical disorders considered in the comparisons. This is true overall as well as for the vast majority of the 100 pair-wise disorder comparisons in the total sample as well as separately among treated cases and separately among untreated cases. Second, the findings document that mental disorders have somewhat different cross-domain profiles of role impairment than the chronic medical disorders, with the impairments of mental disorders significantly greater than those for the chronic medical disorders in the domains of home, social, and close relationships, but not in the domain of work. Third, the findings document that comorbidity between chronic medical and mental disorders plays an important role in the impairments associated with both types of disorder.
Before discussing these findings, it is important to address two major study limitations. First, the NCS-R relied on self-report to quantify the degree of impairment associated with the disorders considered here. As noted above in the section on measurement, this concern is somewhat mitigated by the fact that within the NCS-R, we found a strong and consistent gradient between severity of Sheehan scores and mean days out of role for mental (r=0.59) and chronic medical (r=0.61) disorders (full results available from the authors on request). Also, within-person medical-mental comparisons in the sub-sample of respondents who both had one or more chronic medical disorders and one or more mental disorders yielded results very similar to those found in the total sample. This is an important finding because it shows that elevated perceptions of impairment associated with having the mental disorder do not account for physical-mental differences as within-person analyses should control for any such individual differences. Finally, as noted above, comparable results have been reported in studies that used other validated indicators of impairment.21, 39
Second, while a structured diagnostic instrument was used to identify mental disorders, chronic medical conditions were identified via self-report, raising the possibility that lower validity of diagnostic assessment for the chronic medical disorders than the mental disorders might have biased results against finding high impairment associated with the chronic medical disorders. It is noteworthy in this regard that previous studies have shown that patient-reported diagnoses of chronic medical disorders have generally been found to correlate well with physician diagnosis in methodological studies aimed at validating the data reported in chronic conditions checklists.31
Furthermore, the consistency of the study findings across both treated and untreated individuals provides further support for the validity of the relative differences in role impairment between mental and chronic medical conditions.
With these methodological considerations as a backdrop, it is noteworthy that data on the high burden of mental disorders, particularly estimates from the World Health Organization’s Global Burden of Disease Study,41
have been embraced by mental health advocates and policymakers as evidence that mental disorders are more burdensome than most chronic medical disorders.42, 43
The current study further documents the high relative impairment, as well as the low treatment rates, associated with mental disorders in the United States. Coupled with data on the favorable cost-effectiveness of treatments for mental disorders,44
these findings suggest that mental disorders warrant prioritization in discussions about healthcare resource allocation in the United States. Consistent with this thinking, the Institute of Medicine has ranked both major depression and serious mental illnesses as among the highest priority conditions for US quality improvement initiatives based on evidence of burden and treatment cost-effectiveness.45
It is likely that a more broad-based analysis would lead other commonly-occurring mental disorders to be added to this list.
Our current results support the notion that while both mental and chronic medical disorders lead to considerable impairment, that they do so via different pathways. Chronic medical disorders commonly limit ability to perform basic physical tasks such as activities of daily living, which in turn may impede work and home functioning. Consistent with this mechanism and with previous literature,46
a detailed inspection of our results shows that chronic pain disorders are associated with particularly high levels of work impairment. Mental disorders, in comparison, have their greatest adverse effects on social functioning and close relationships. The latter are high-order functions that are commonly dysregulated by emotional problems.43
This finding is consistent with data from clinical populations, where disproportionate impairments due to mental disorders have been documented in the areas of social and interpersonal role functioning.16, 47
Problems in these domains may be less easily seen and quantified than the deficits resulting from chronic medical disorders, resulting in a substantial “invisible” societal burden.48
Finally, the findings reported here highlight the importance of comorbidity in impairment. Previous studies have documented the fact that increasing numbers of comorbid conditions are associated with increasing likelihood and severity of disability.2, 17
The current study adds to this literature by demonstrating that having a second category of condition may increase the impairment associated with any single index disorder, with a synergistic effect between mental and chronic medical disorders. Individuals who suffer from only a single class of disorder may be still be able to function by relying on other intact domains of functioning to make up for deficits in a single domain. The presence of morbidity across different classes of disorders, though, may reduce this compensatory capacity, resulting in a higher level of impairment for the index disorder than in the absence of comorbidity. The importance of comorbidity is further highlighted by the fact that many of the most disabling conditions in this survey, such as chronic pain syndromes, may both be exacerbated by, and also be a risk factor for, mental symptomatology.
The first conclusion of the 2003 President’s New Freedom Commission on Mental Health was that mental health is essential to overall health.49
The current study presents clear and convincing evidence to support that assertion. Furthermore, the results indicate a serious mismatch between the high degree of impairment and low rate of treatment for mental disorders in the United States. Efforts to reduce disability will need to address mental disorders’ disproportionate burden, distinct patterns of deficits, and the potentially synergistic impact of comorbid mental and chronic medical disorders on impairment.