Tennant, PWG, Arnold, KF, Ellison, GTH orcid.org/0000-0001-8914-6812 et al. (1 more author) (2022) Analyses of 'change scores' do not estimate causal effects in observational data. International Journal of Epidemiology, 51 (5). pp. 1604-1615. ISSN 0300-5771
Abstract
Background In longitudinal data, it is common to create ‘change scores’ by subtracting measurements taken at baseline from those taken at follow-up, and then to analyse the resulting ‘change’ as the outcome variable. In observational data, this approach can produce misleading causal-effect estimates. The present article uses directed acyclic graphs (DAGs) and simple simulations to provide an accessible explanation for why change scores do not estimate causal effects in observational data.
Methods Data were simulated to match three general scenarios in which the outcome variable at baseline was a (i) ‘competing exposure’ (i.e. a cause of the outcome that is neither caused by nor causes the exposure), (ii) confounder or (iii) mediator for the total causal effect of the exposure variable at baseline on the outcome variable at follow-up. Regression coefficients were compared between change-score analyses and the appropriate estimator(s) for the total and/or direct causal effect(s).
Results Change-score analyses do not provide meaningful causal-effect estimates unless the baseline outcome variable is a ‘competing exposure’ for the effect of the exposure on the outcome at follow-up. Where the baseline outcome is a confounder or mediator, change-score analyses evaluate obscure estimands, which may diverge substantially in magnitude and direction from the total and direct causal effects.
Conclusion Future observational studies that seek causal-effect estimates should avoid analysing change scores and adopt alternative analytical strategies.
Metadata
Item Type: | Article |
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Authors/Creators: |
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Copyright, Publisher and Additional Information: | © The Author(s) 2021. Published by Oxford University Press on behalf of the International Epidemiological Association. 1604 This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited. |
Keywords: | Analysis of change; change scores; difference scores; gain scores; change-from-baseline variables; directed acyclic graphs |
Dates: |
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Institution: | The University of Leeds |
Academic Units: | The University of Leeds > Faculty of Medicine and Health (Leeds) > School of Medicine (Leeds) > Leeds Institute of Cardiovascular and Metabolic Medicine (LICAMM) > Clinical & Population Science Dept (Leeds) |
Depositing User: | Symplectic Publications |
Date Deposited: | 07 May 2024 13:26 |
Last Modified: | 07 May 2024 13:26 |
Status: | Published |
Publisher: | Oxford University Press |
Identification Number: | 10.1093/ije/dyab050 |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:148578 |