Covariate adjustment and prediction of mean response in randomised trials

Last week I attended the International Society for Clinical Biostatistics' conference in Vigo, Spain. I spoke about work I've been doing recently on covariate adjusted mean estimation in randomised trials. A pre-print draft of the work is available at arXiv.

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Imputing missing covariates in nested case-control and case cohort studies

I'm pleased to announce a new version (1.3.0) of the smcfcs package for multiple imputation of missing covariates. Thanks to Ruth Keogh at the London School of Hygiene & Tropical Medicine, this new version features two additional functions, smcfcs.casecohort and smcfcs.nestedcc. These allow for imputing of missing covariates in case cohort and nested case-control studies respectively. A paper describing the methodology is forthcoming.

The package is now on CRAN and so can be installed/updated in the usual way from R or RStudio.

There are of course various papers on the case cohort and nested case control study designs. For further reading, I'd recommend looking at Ruth's book, co-authored with David Cox, 'Case-Control Studies', which contains a chapter on each design.

Odds ratios, collapsibility, marginal vs. conditional, GEE vs GLMMs

Generalised estimating equations (GEEs) and generalised linear mixed models (GLMMs) are two approaches to modelling clustered or longitudinal categorical outcomes. Here I will focus on the common setting of a binary outcome. As is commonly described, the two approaches estimate different effect measures, with GEEs targeting so called marginal effects, and GLMMs targeting conditional or subject specific effects. Understanding the difference between these is potentially quite tricky I think.

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Handling competing risks in randomized trials

Peter Austin and Jason Fine (of Fine & Gray fame) have just published a nice review article in Statistics in Medicine on handling competing risks in randomized trials. They reviewed RCTs published in four top medical journals in the last three months of 2015. Of the 40 trials found with time to event outcomes, Austin & Gray determined that 31 were potentially susceptible to competing risks.

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Frequentists should more often consider using Bayesian methods

Recently my colleague Ruth Keogh and I had a paper published: 'Bayesian correction for covariate measurement error: a frequentist evaluation and comparison with regression calibration' (open access here). The paper compares the popular regression calibration approach for handling covariate measurement error in regression models with a Bayesian approach. The two methods are compared from the frequentist perspective, and one of the arguments we make is that frequentists should more often consider using Bayesian methods.

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