New or variant treatments—and we use the word in a wide sense to include procedures and devices as well as drugs—should be subject to randomised controlled trials.1 Treatments may also develop, changing in ways that are widely considered to be improvements. For example, a new version of a surgically fitted device supersedes the old. This complicates existing comparisons of the device compared with medical treatment. And it leads to another issue—when should researchers start a randomised controlled trial in a clinical area where there is rapid technological change? Start too early and the resultant comparisons may seem likely to turn out to be irrelevant, but start too late and the chance of collecting much good quality data will have been lost, perhaps forever if clinical opinion has “gelled” despite the absence of randomised controlled trial data. The problem is compounded by the considerable time it takes to design, commission, and establish a full scale clinical trial.

These problems are encountered widely, particularly with devices. These may be licensed even before their health effects have been studied in detail and are subject to frequent modifications in design and use. A good example is endovascular aortic aneurysm repair, in which a Dacron tube is positioned within the abdominal aorta and held in place by an expandable stent. In 1991, Parodi et al showed that aneurysms could be repaired in this way.2 Several stent graft systems have emerged since then, with changes occurring almost monthly.

In these circumstances useful evaluation by randomised controlled trial evaluation might be thought impossible, and researchers and commissioners might choose to wait for things to stabilise.3 In this paper we argue against waiting and advocate the use of trials which start early on in periods of rapid technological change and which follow and inform developments. …