Commentary on Instrumental Variable Methods for Low Compliance

Abstract

A recent editorial in the British Journal of Sports Medicine (BJSM) suggested instrumental var-iable (IV) analysis has advantages in estimating causal effects when there is low compliance. We originally submitted a version of this commentary to BJSM as an editorial (they do not have a letter to editor section) but it was rejected without review. The original BJSM editorial included several important errors, presented results that are inconsistent with the results of an IV analysis, and omitted definitions and important limitations. All of these factors contrib-uted to inappropriate interpretations. This commentary highlights the most important er-rors. We also believe the BJSM editorial serves as another reminder that appropriate statisti-cians should be included from the beginning of the study wherever possible. At the very least, they should be the co-authors responsible for calculating results and ensuring the write-up is consistent with the results.