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Main Authors: Bartlett, Jonathan W., Magirr, Dominic, Morris, Tim P.
Format: Preprint
Published: 2026
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Online Access:https://arxiv.org/abs/2601.09571
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author Bartlett, Jonathan W.
Magirr, Dominic
Morris, Tim P.
author_facet Bartlett, Jonathan W.
Magirr, Dominic
Morris, Tim P.
contents The hazard ratio, typically estimated using Cox's famous proportional hazards model, is the most common effect measure used to describe the association or effect of a covariate on a time-to-event outcome. In recent years the hazard ratio has been argued by some to lack a causal interpretation, even in randomised trials, and even if the proportional hazards assumption holds. This is concerning, not least due to the ubiquity of hazard ratios in analyses of time-to-event data. We review these criticisms, describe how we think hazard ratios should be interpreted, and argue that they retain a valid causal interpretation. Nevertheless, alternative measures may be preferable to describe effects of exposures or treatments on time-to-event outcomes.
format Preprint
id arxiv_https___arxiv_org_abs_2601_09571
institution arXiv
publishDate 2026
record_format arxiv
spellingShingle How to interpret hazard ratios
Bartlett, Jonathan W.
Magirr, Dominic
Morris, Tim P.
Methodology
The hazard ratio, typically estimated using Cox's famous proportional hazards model, is the most common effect measure used to describe the association or effect of a covariate on a time-to-event outcome. In recent years the hazard ratio has been argued by some to lack a causal interpretation, even in randomised trials, and even if the proportional hazards assumption holds. This is concerning, not least due to the ubiquity of hazard ratios in analyses of time-to-event data. We review these criticisms, describe how we think hazard ratios should be interpreted, and argue that they retain a valid causal interpretation. Nevertheless, alternative measures may be preferable to describe effects of exposures or treatments on time-to-event outcomes.
title How to interpret hazard ratios
topic Methodology
url https://arxiv.org/abs/2601.09571