Background
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EVENTS, EVENT
A common intercurrent event affecting many randomised controlled trials (RCTs) is when some participants do not begin the treatment they were randomised to.Many trials use a ‘modified intention-to-treat’ (mITT) approach to handle these intercurrent events in the analysis, whereby participants who do not initiate treatment are excluded (i.e. the analysis is performed only on the participants who initiate treatment).Given the widespread use of mITT in practice, there is urgent need to define the target estimand for such an approach, as well as the settings in which it will be unbiased. The purpose of this article is therefore to (a) demonstrate that an mITT estimator which excludes participants who do not begin treatment targets a 