Comparing Alternative Effect Decomposition Methods

Abstract

Background Inverse odds ratio weighting, a newly proposed tool to evaluate mediation in exposure-disease associations, may be valuable for a host of research questions but little is known about its performance in real data. We compare this approach to a more conventional Baron and Kenny decomposition on an additive hazards scale to estimate total, direct, and indirect effects using the example of the role of literacy in mediating the effects of education on mortality. Methods Health and Retirement Study participants born in the U.S. between 1900 and 1947 were interviewed biennially for up to 12 years (N=17,054). Literacy was measured with a brief vocabulary assessment. Decomposition estimates were derived based on Aalen additive hazards models. Results A one standard deviation difference in educational attainment (3 years) was associated with 6.7 fewer deaths per 1,000 person-years (β=-6.7, 95% CI: -7.9, -5.4). Of this decrease, 1.3 fewer deaths (β=-1.3, 95% CI: -4.0, 1.2) were attributed to the literacy pathway (natural indirect), representing 19% of the total effect. Baron and Kenny estimates were consistent with inverse odds ratio weighting estimates but were more precise (natural indirect effect: -1.2 (95% CI: -1.7, -0.69, representing 18% of total effect). Conclusion In a cohort of older Americans, literacy partially mediated the effect of education on mortality.

Effect modification, interaction and mediation: an overview of theoretical insights for clinical investigators

“…Standard approaches to assess mediation do not allow to accommodate a possible mediator–exposure interaction 45. Nonstandard, newer approaches are conceptually complicated, and as yet not completely settled 24,46. As such, researchers have to assume no mediator–exposure interaction (or relax this assumption).…”

The role of literacy in the association between educational attainment and depressive symptoms

“…Literacy, assessed using a vocabulary test, was the mediator of focus. This measure has been previously described, and we coded this variable as we have in our previous research ( Nguyen et al, 2016 ). Beginning in Wave 3 (1995/6), respondents were presented with a set of 5 vocabulary words associated with increasing literacy demand, and were asked to define each word.…”

“…Non-parametric bootstrapping is used to obtain ninety-five percent confidence intervals for the total, NDE and NIE. For further details on the odds ratio formula with continuous variables, please see ( Nguyen et al, 2016 ). For an application of this approach using a binary exposure, please see ( Nguyen, Osypuk, Schmidt, Glymour, & Tchetgen Tchetgen, 2015 ).…”

“…We next corrected for measurement error in our vocabulary assessment using the WRAT as validation data in implementing the measurement correction approach for IORW. Additional details and the mathematical proof for the measurement error correction has been published elsewhere ( Nguyen et al, 2016 ). Briefly, we performed the following steps to implement the modified IORW approach.…”

“…Literacy has also been shown to partially mediate the link between education and hypertension knowledge but not hypertension control ( Pandit et al, 2009 ). Recently published work indicated that literacy partially mediates the relationship between education and mortality ( Nguyen et al, 2016 ). To the authors’ knowledge, these remain the only published studies formally evaluating literacy as a mediator between education and health, and no prior work has evaluated the role of literacy in mediating effects of education on mental health outcomes.…”