Systematic reviews of randomised controlled trials provide an evidence base for treatment but too often fail to give adequate information on long term outcomes. Elphick and colleagues discuss the limitations of the systematic review of randomised controlled trials for patients with chronic or lifelong diseases and suggest that long term observational studies have a place in the evaluation of the benefits and risks of treatment

Synthesis of evidence from systematic reviews of randomised controlled trials is considered thegold standard when evaluating the effectiveness of treatments, yet systematic reviews do not always place as much emphasis on information about adverse effects or safety issues. 1 2 In people with chronic, or lifelong,diseases long term outcomes are particularly important but are much less likely to be evaluated inrandomised controlled trials. We discuss the results of a recent systematic review of randomised controlled trials of antibiotic therapy in cystic fibrosis, which provided preliminary information about antibiotic resistance but not about other adverse effects. Although the review suggested that this finding should be investigated by a further clinical trial, we discuss why this may be neither the most feasible nor the most efficient study design with which to evaluate long term outcomes in lifelong diseases.