Should data and safety monitoring boards share confidential interim data?

Consider the following situation: Two clinical trials are underway, closely related in terms of the interventions being compared and the target popula tions. In preparing for a planned interim analysis, the statistician for tr ial 1 finds that the results support a recommendation to stop the trial ear ly. Should the statistician ask the investigators for trial 2 to make inter im results of their trial available to the data and safety monitoring board (DSMB) for trial 1? If so, in what form? Would the answers change if the t rial 1 results showed a strong but not convincing trend? What is the obliga tion of the trial 2 investigators to respond to such a request? What role d o the two DSMBs have, either in initiating a request or in agreeing to resp ond to it? In this article, we examine this situation in some detail, havin g faced it occasionally in our own experience with clinical trials and DSMB s. The chief argument in favor of sharing data is that data from trial 2 ar e obviously relevant to the question being addressed by trial 1 and therefo re ought to be available to those who must interpret the results from that trial. On the other hand, there are several reasons for not sharing interim data. For example, sharing is incompatible with the independence of the tr ials; the time for synthesizing evidence from both trials is after the two teams of investigators have presented the full analysis and interpretation of their separate trials. For this and other conceptual and practical reaso ns we conclude that it is better, in most cases, for DSMBs to consider only information that has already been made public in some form. Control Clin T rials 2000;21:1-6 (C) Elsevier Science Inc. 2000.