The authors' analysis of quality improvement strategies for diabetes care showed no particular type of QI to have an advantage over others, but suggested that employing at least two strategies provides a greater chance of success than single-faceted interventions, in terms of improving glycemic control or provider adherence. These conclusions are limited by probable publication bias favoring smaller trials and non-randomized trials, and the confounding presence of multiple QI strategies in a given intervention, as well as important patient and provider factors, and organizational characteristics.