September 1, 2026The Lancet
External validity of randomised controlled trials: “To whom do the results of this trial apply?”
Authors
Discussion
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Implication
Methodological review reveals substantial barriers to external validity in clinical trial cohorts, highlighting limited applicability to real-world patients.
Key Points
- To examine the key determinants of external validity in randomised controlled trials and evaluate why trial results frequently fail to translate to routine clinical practice.
- Reviewed methodological literature and trial reporting practices regarding trial design factors that constrain generalisability.
- Assessed disparities between clinical trial cohorts and real-world populations across patient selection, intervention delivery, and healthcare settings.
- Highly restrictive eligibility criteria commonly exclude the vast majority of regular clinical patients, particularly older individuals and those with common comorbidities.
- Inadequate reporting of setting, clinician expertise, and baseline characteristics limits clinicians' ability to evaluate whether published trial results apply to their patients.
Cite This Study
Peter M. Rothwell (2005) studied this question.