The quantity of research into patient safety has risen substantially over the past decade.1 Nevertheless, concerns remain over the quality of much of this research2 and there are disagreements about methods.3 As a result, the Medical Research Council sponsored a cross council research network in patient safety research to provide methodological guidance on evaluation of patient safety interventions. This resulted in publication of a series of articles in Quality and Safety in Health Care.4 5 6 7 Here we summarise two main themes developed in the series: study design and determining what observations should be made.

It is not possible to cleanly separate safety interventions from quality improvements.4 That said, the term safety is typically used in the context of rare incidents where there is a rapid and strong link between an error and its associated outcome. Our comments therefore apply to both safety and quality improvement but take into account the rarity of many safety incidents. Safety interventions are directed at the system in which care is delivered. They are thus service delivery interventions not new health technologies. Such interventions are often complex and should be evaluated before implementation (alpha testing), as advocated by both the …