All I want for Christmas…is a precisely defined research question

This Christmas, five years on from the publication of the International Conference on Harmonisation E9 Addendum on Estimands and Sensitivity Analysis in Clinical Trials (ICH E9 (R1) addendum), we describe a fictitious, festive randomised controlled trial conducted by Santa Claus to answer the question: does a reindeer’s pre-flight meal impact performance? It is important that all clinical trials are designed, conducted and analysed to address clear and meaningful research questions. To address this, the ICH E9 (R1) addendum introduced the estimand framework. These guidelines clarified the importance of precisely defining the treatment effects targeted in trials of health care interventions by using estimands. However, estimands can be challenging to understand and appreciate. We use this fictitious example to explain what an estimand is and demonstrate why there is a need for their use, turning Santa’s initial vague research question into a more precise question in line with the addendum by using estimands. Whilst light-hearted in nature we hope that this article will facilitate application of the international trial guidelines (ICH E9 (R1)) that are now adopted worldwide and require the use of estimands.