Disability mediates the impact of common conditions on perceived health

Abstract

Background: We examined the extent to which disability mediates the observed associations of common mental and physical conditions with perceived health.

Methods and findings: WHO World Mental Health (WMH) Surveys carried out in 22 countries worldwide (n = 51,344 respondents, 72.0% response rate). We assessed nine common mental conditions with the WHO Composite International Diagnostic Interview (CIDI), and ten chronic physical with a checklist. A visual analog scale (VAS) score (0, worst to 100, best) measured perceived health in the previous 30 days. Disability was assessed using a modified WHO Disability Assessment Schedule (WHODAS), including: cognition, mobility, self-care, getting along, role functioning (life activities), family burden, stigma, and discrimination. Path analysis was used to estimate total effects of conditions on perceived health VAS and their separate direct and indirect (through the WHODAS dimensions) effects. Twelve-month prevalence was 14.4% for any mental and 51.4% for any physical condition. 31.7% of respondents reported difficulties in role functioning, 11.4% in mobility, 8.3% in stigma, 8.1% in family burden and 6.9% in cognition. Other difficulties were much less common. Mean VAS score was 81.0 (SD = 0.1). Decrements in VAS scores were highest for neurological conditions (9.8), depression (8.2) and bipolar disorder (8.1). Across conditions, 36.8% (IQR: 31.2-51.5%) of the total decrement in perceived health associated with the condition were mediated by WHODAS disabilities (significant for 17 of 19 conditions). Role functioning was the dominant mediator for both mental and physical conditions. Stigma and family burden were also important mediators for mental conditions, and mobility for physical conditions.

Conclusions: More than a third of the decrement in perceived health associated with common conditions is mediated by disability. Although the decrement is similar for physical and mental conditions, the pattern of mediation is different. Research is needed on the benefits for perceived health of targeted interventions aimed at particular disability dimensions.

Figure 1. General mediation model used in analyses.

The figure displays the general mediation model that has been used to estimate effects according to path-diagrammatic conventions. Squares represent variables. D_i is one of the p = 19 disorders under consideration, M_j is one of the k = 8 mediating variables (disability dimensions), and VAS is the final outcome. Arrows represent regression slope parameters from independent variables to outcomes. The δ parameters stand for the direct effect regression from disorders to the final outcome. The ι parameters indicate the two regression components of the disorder indirect effects as mediated by M: a) p x k regression parameters from D to M (ι_Dij) and b) k regression parameters from M to VAS (ι_{M j}). For each disorder the model can be decomposed in two paths: 1) VAS regressed on disorders, and 2) a causal mediation chain of VAS regressed on mediators which in turn are regressed on disorders. The partial indirect effect of a certain disorder D_i through a mediator M_j is ι_Dij x ι_Mj, whereas its total indirect effect is the sum of the k products across mediators (). Total effects for a disorder are the sum of direct and total indirect effect (δ_i+Ι_i). Directionality cannot be assumed as a causal association in our study due to its cross-sectional, observational nature. Also notice that in the general model, the effect of each disorder on each mediator is adjusted by the direct effect of the remaining disorders (thus controlling for comorbidity), while the impact of a disorder on VAS is controlled by the total effects of the other disorders. Disability is thus fully taken into account, even though it is decomposed in subscales. The effects on VAS are also controlled for age, gender, employment status and country.

Figure 2. Direct and indirect effects (via WHODAS dimensions) of common chronic conditions on perceived health VAS, overall sample.

WMH Surveys.

Figure 3. Relative WHODAS dimension contributions to the indirect effect of disability on perceived health VAS for each condition, overall sample.

WMH Surveys (Alcohol Abuse and Drug Abuse are not represented because their respective overall indirect effect is not significant).