Efficacy assessed in follow-ups of clinical trials: methodological conundrum
Maastricht University Medical Center, Department of Internal Medicine, Rheumatology, P.O. Box 5800, 6202AZ Maastricht, The Netherlands
Arthritis Research & Therapy 2010, 12:132 doi:10.1186/ar3080
See related research by Rantalaiho et al., http://arthritis-research.com/content/12/3/R122Published: 30 July 2010
Increasingly, we see papers describing the long-term follow-up results of randomised clinical trials. Sometimes, like the article by Rantalaiho and colleagues in the previous issue of Arthritis Research & Therapy, the follow-up extends to more than 10 years. It is not uncommon that authors of such articles describe their results as a comparison of the original treatment groups in the original randomised clinical trial. Methodologically, such a comparison is fallible for several reasons. In this editorial, two important sources of bias that may jeopardise the results of such follow-up studies are discussed: confounding by indication and confounding by trial completion.