Implications for trials in progress of publication of positive results.

It is not easy to decide, when results from similar trials appear, whether a trial still underway should be stopped or not. The weight of the other evidence has to be taken into account--as indeed it has to be for decisions by clinicians and by health service managers outside the settings of a trial. Taking the Systolic Hypertension in the Elderly Trial (SHEP) as an example, we show how its results are not unequivocal (ie, there is no proof beyond reasonable doubt). This verdict justifies the continuation of similar trials in progress. More generally--but again for individual clinicians and for trial organisers and again with SHEP as the example--we illustrate a bayesian approach to trial-termination decisions.