Factors That Can Affect the External Validity of Randomised Controlled Trials

Citation: Rothwell, P. M. (2006). 'Factors that can affect the external validity of randomised controlled trials' PLoS Clinical Trials, 1(1): e9. [Available at http://clinicaltrials.ploshubs.org]. Copyright 2006 Peter M. Rothwell. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.