Collider Bias Is Only a Partial Explanation for the Obesity Paradox

Sperrin, Matthew, Candlish, Jane, Badrick, Ellena, Renehan, Andrew and Buchan, Iain ORCID: 0000-0003-3392-1650
(2016) Collider Bias Is Only a Partial Explanation for the Obesity Paradox. Epidemiology, 27 (4). pp. 525-530.

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Background: “Obesity paradox” refers to an association between obesity and reduced mortality (contrary to an expected increased mortality). A common explanation is collider stratification bias: unmeasured confounding induced by selection bias. Here, we test this supposition through a realistic generative model. Methods: We quantify the collider stratification bias in a selected population using counterfactual causal analysis. We illustrate the bias for a range of scenarios, describing associations between exposure (obesity), outcome (mortality), mediator (in this example, diabetes) and an unmeasured confounder. Results: Collider stratification leads to biased estimation of the causal effect of exposure on outcome. However, the bias is small relative to the causal relationships between the variables. Conclusions: Collider bias can be a partial explanation of the obesity paradox, but unlikely to be the main explanation for a reverse direction of an association to a true causal relationship. Alternative explanations of the obesity paradox should be explored. See Video Abstract at

Item Type: Article
Uncontrolled Keywords: Humans, Obesity, Mortality, Logistic Models, Bias, Confounding Factors, Epidemiologic
Depositing User: Symplectic Admin
Date Deposited: 26 Mar 2019 16:44
Last Modified: 15 Mar 2024 15:24
DOI: 10.1097/EDE.0000000000000493
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