Halting high profile trials early has been in the news again this year.1 Legitimate questions have been raised about who decides that a trial should stop early, how they do it, and on what basis they reach such a decision.

Nearly all ongoing randomised clinical trials need some form of data monitoring.2^–4 Differences between treatments may be larger than expected or unanticipated adverse effects may occur, and either of these may justify early termination of a trial. Although this has obvious bearing on current and potential participants in the trial, it also has potentially profound wider implications. In particular, the data from the trial may later constitute the evidence base for management of future patients. Hence the data should be sufficiently convincing to the wider clinical and patient community to determine future practice. Those taking a decision to stop a trial early therefore carry a heavy responsibility for ensuring that this would be in the best interests both of the individuals involved in the trial and of society.

Currently only a minority of trials have a formal group, often called a data monitoring committee, whose remit is to monitor a trial's data as they accumulate, …