Finding and filling the gaps in the evidence with high quality clinical trials - the experience of one Cochrane Review Group.

The Cochrane Cystic Fibrosis and Genetic Disorders Group publishes systematic reviews of randomized trials for many genetic disorders. Given the rarity of these disorders, there are often few relevant trials to be included. Therefore, it is common for the reviews to be 'empty' and unable to present evidence which aids decision-making in clinical practice. However, we do not regard this as negative; rather we see this as a challenge and an opportunity to influence the research agenda. We have several reviews which clearly illustrate the cycle of assessing the evidence base, identifying the lack of data, generating high quality research and incorporating the resulting data into the original systematic review.