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IJE Advance Access published online on September 23, 2009
International Journal of Epidemiology, doi:10.1093/ije/dyp305
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Published by Oxford University Press on behalf of the International Epidemiological Association © The Author 2009; all rights reserved.

Commentary: External validity of results of randomized trials: disentangling a complex concept

Peter M Rothwell

University Department of Clinical Neurology, Level 6, West Wing, John Radcliffe Hospital, Headington, Oxford OX3 9DU, UK. E-mail: peter.rothwell@clneuro.ox.ac.uk

Accepted 25 August 2009

The first 10% of the full text of this article appears below.

It is now widely accepted that in most situations, randomized controlled trials (RCTs) and systematic reviews are the most reliable methods of determining the effects of treatment. Yet, the methodology is still relatively new (a few decades old), and so our understanding of trial design, and more especially of how best to make use of results, is less than perfect. RCTs must be internally valid (i.e. their design and conduct must minimize the possibility of bias), and, until recently, guidelines on trial methodology and reporting, such as the CONSORT initiative, concentrated almost completely on issues related to internal validity. However, to be clinically useful, the result of a trial must . . . [Full Text of this Article]


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