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J Clin Epidemiol. 2011 May;64(5):471-80. doi: 10.1016/j.jclinepi.2010.05.009. Epub 2010 Oct 8.

Aggregating single patient (n-of-1) trials in populations where recruitment and retention was difficult: the case of palliative care.

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The University of Queensland, Discipline of General Practice, Queensland, Australia, South Australia.


Randomized controlled trials (RCTs) are the gold standard for evaluating new interventions. Different RCT designs apply depending on the patient population, clinical setting, and intervention being evaluated. A design that may help to generate evidence in some clinical areas where recruitment is a challenge is aggregated n-of-1 trials. N-of-1 trials are randomized, double-blind, and multiple crossover comparisons of an intervention and a control treatment. Methodologically robust n-of-1 trials provide an objective means of testing the effectiveness of treatments within individual participants. Aggregation of multiple cycle identically conducted n-of-1 trials yield a population estimate of effect, which potentially commensurate with that derived from other RCT designs. Trial participants contribute data for both intervention and control treatments creating matched data sets while using generally smaller sample sizes than conventional RCT trials. Careful choice of symptoms and medications are required for n-of-1 trials to be feasible. A validated and reliable outcome measure sensitive to change is still required. This article reviews the utility and limitations of aggregated n-of-1 trials to gather evidence in populations where conducting formal RCTs is difficult because of the low prevalence of the underlying condition or the clinical condition making recruitment and retention difficult. The article examines a proposed palliative care trial as a test case.

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