Analysing trajectories of a longitudinal exposure: A causal perspective on common methods in lifecourse research

Levine, S. Z., Gadd, S. C., Tennant, P. W. G., Heppenstall, A. J. , Boehnke, J. R. and Gilthorpe, M. S. (2019) Analysing trajectories of a longitudinal exposure: A causal perspective on common methods in lifecourse research. PLoS ONE, 14(12), e0225217. (doi: 10.1371/journal.pone.0225217) (PMID:31800576) (PMCID:PMC6892534)

Abstract

Longitudinal data is commonly analysed to inform prevention policies for diseases that may develop throughout life. Commonly methods interpret the longitudinal data as a series of discrete measurements or as continuous patterns. Some of the latter methods condition on the outcome, aiming to capture ‘average’ patterns within outcome groups, while others capture individual-level pattern features before relating these to the outcome. Conditioning on the outcome may prevent meaningful interpretation. Repeated measurements of a longitudinal exposure (weight) and later outcome (glycated haemoglobin levels) were simulated to match three scenarios: one with no causal relationship between growth rate and glycated haemoglobin; two with a positive causal effect of growth rate on glycated haemoglobin. Two methods that condition on the outcome and one that did not were applied to the data in 1000 simulations. The interpretation of the two-step method matched the simulation in all causal scenarios, but that of the methods conditioning on the outcome did not. Methods that condition on the outcome do not accurately represent a causal relationship between a longitudinal pattern and outcome. Researchers considering longitudinal data should carefully determine if they wish to analyse longitudinal data as a series of discrete time points or by extracting pattern features.

• Item Type: Articles
• Additional Information: This work was supported by the Economic and Social Research Council (esrc.ukri.org) [ES/P000746/1 to S.C.G.]; and the Alan Turing Institute (turing.ac.uk) [EP/N510129/1 to P.W.G.T. and M.S.G., ES/R007918/1 to A.H.].
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Heppenstall, Professor Alison
• Authors: Levine, S. Z., Gadd, S. C., Tennant, P. W. G., Heppenstall, A. J., Boehnke, J. R., and Gilthorpe, M. S.
• College/School: College of Social Sciences > School of Social and Political Sciences > Urban Studies
• Journal Name: PLoS ONE
• Publisher: Public Library of Science
• ISSN: 1932-6203
• ISSN (Online): 1932-6203
• Copyright Holders: Copyright © 2019 Gadd et al.
• First Published: First published in PLoS ONE 14(12):e0225217
• Publisher Policy: Reproduced under a creative commons licence