Covariate adjustment and estimation of mean response in randomised trials

Jonathan W Bartlett

Research output: Contribution to journalArticlepeer-review

14 Citations (SciVal)
114 Downloads (Pure)


Analyses of randomised trials are often based on regression models which adjust for baseline covariates, in addition to randomised group. Based on such models, one can obtain estimates of the marginal mean outcome for the population under assignment to each treatment, by averaging the model-based predictions across the empirical distribution of the baseline covariates in the trial. We identify under what conditions such estimates are consistent, and in particular show that for canonical generalised linear models, the resulting estimates are always consistent. We show that a recently proposed variance estimator underestimates the variance of the estimator around the true marginal population mean when the baseline covariates are not fixed in repeated sampling and provide a simple adjustment to remedy this. We also describe an alternative semiparametric estimator, which is consistent even when the outcome regression model used is misspecified. The different estimators are compared through simulations and application to a recently conducted trial in asthma.

Original languageEnglish
Pages (from-to)648-666
Number of pages19
JournalPharmaceutical Statistics
Issue number5
Early online date11 Jul 2018
Publication statusPublished - 1 Sept 2018

ASJC Scopus subject areas

  • Statistics and Probability
  • Pharmacology
  • Pharmacology (medical)


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