Stephen’s main area of research is causal inference and specifically methods for Mendelian randomization: the use of genetic variants to understand whether putative risk factors are causally related to specific disease outcomes (target validation).

In 2013, Stephen was awarded a Wellcome Trust entry-level fellowship (Sir Henry Wellcome Post-doctoral Fellowship) to continue theoretical and applied work in the field of Mendelian randomization. In 2017, he moved to the MRC Biostatistics Unit on a Wellcome Trust/Royal Society intermediate fellowship (Sir Henry Dale Fellowship) to establish a research group in the MRC Biostatistics Unit, where he is now a Programme Leader. In 2023, he was given a Career Development Award by the Wellcome Trust to continue work in this area. He leads a small team of researchers split between the MRC Biostatistics Unit and the Cardiovascular Epidemiology Unit. 

Shaun’s research interests include methodology for drawing causal inferences from observational data and for handling selection biases and missing data.  A causal inference problem that particularly interests Shaun is time-dependent confounding.  This arises when a time-varying exposure (e.g. treatment) is affected by time-varying confounders that are themselves affected by the exposure.  This confounding complicates the estimation of treatment effects and the identification of optimal treatment regimes for individual patients.