Background: In primary care, most interventions aimed at improving patient care involve those providing it and are complex in nature. Cluster-randomized controlled trials (c-RCTs) are common because they take into account the special structure of these studies. However, they also require a lot of effort to design and conduct.
Objectives: The aim of this study was thus to assess how often c-RCTs dealing with complex interventions were able to show significant improvements over routine care. Furthermore, we investigated potential quality differences between studies showing an effect and those that did not.
Methods: We searched MEDLINE and the Cochrane Database of Systematic Reviews for c-RCTs published in eight journals (BMJ, British Journal of General Practice, Family Practice, Preventive Medicine, Annals of Internal Medicine, Journal of General Internal Medicine, Paediatrics, Canadian Medical Journal) from 1946 to April 2014. We considered c-RCTs of complex interventions in general practices that had at least one-year follow-up and included a patient-relevant primary outcome. For each study, we assessed the effectiveness of its intervention and the reporting of 18 quality criteria.
Results: We found 21 papers that fulfilled our inclusion criteria, seven of which (33%) showed an intervention effect for at least one primary outcome; four showed an effect for some but not all primary outcomes; and three for all. The latter studies all accounted for the clustered structure of the study in both sample size calculation and statistical analysis. Information on general quality criteria such as cluster consent, trial registration or publication of study protocol was also reported more rigorously in those studies.
Conclusions: We found that two-thirds of c-RCTs dealing with complex interventions in a primary care setting were unable to provide evidence of improvements in patient care. This has to be kept in mind when designing future studies aimed at improving the current health care system.