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Stat Methods Med Res. 2018 Jan 1:962280218756158. doi: 10.1177/0962280218756158. [Epub ahead of print]

Adjustment for time-invariant and time-varying confounders in 'unexplained residuals' models for longitudinal data within a causal framework and associated challenges.

Author information

1
1 Leeds Institute for Data Analytics, University of Leeds, Leeds, UK.
2
2 School of Medicine, University of Leeds, Leeds, UK.
3
3 Tumor Immunology Lab, Radboud University Medical Centre, Nijmegen, The Netherlands.
4
4 School of Healthcare, University of Leeds, Leeds, UK.
5
5 School of Geography, University of Leeds, Leeds, UK.

Abstract

'Unexplained residuals' models have been used within lifecourse epidemiology to model an exposure measured longitudinally at several time points in relation to a distal outcome. It has been claimed that these models have several advantages, including: the ability to estimate multiple total causal effects in a single model, and additional insight into the effect on the outcome of greater-than-expected increases in the exposure compared to traditional regression methods. We evaluate these properties and prove mathematically how adjustment for confounding variables must be made within this modelling framework. Importantly, we explicitly place unexplained residual models in a causal framework using directed acyclic graphs. This allows for theoretical justification of appropriate confounder adjustment and provides a framework for extending our results to more complex scenarios than those examined in this paper. We also discuss several interpretational issues relating to unexplained residual models within a causal framework. We argue that unexplained residual models offer no additional insights compared to traditional regression methods, and, in fact, are more challenging to implement; moreover, they artificially reduce estimated standard errors. Consequently, we conclude that unexplained residual models, if used, must be implemented with great care.

KEYWORDS:

Unexplained residuals model; causal inference; conditional analysis; conditional growth; conditional regression model; conditional size; conditional weight; directed acyclic graph; lifecourse epidemiology

PMID:
29451093
DOI:
10.1177/0962280218756158
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