Key result
This commentary discusses the importance of external validity and the generalizability of randomized controlled trial results to clinical practice.
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Design
Editorial
Highlights the importance of external validity (applicability to clinical practice) in addition to internal validity when interpreting randomized controlled trials.
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 also be relevant to clinical practice, i.e. be reasonably likely to be replicated when applied to a definable group of patients in a particular clinical setting. The extent to which a result can be extrapolated in this way has been variously termed as ‘external validity, applicability or generalizability’.1
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Peter M. Rothwell (2009) reported an editorial. This commentary discusses the importance of external validity and the generalizability of randomized controlled trial results to clinical practice.