The short answer is there are methods for doing meta-analyses of N-of-1 trials. I have included some references below authored by our colleagues at Tufts, plus an editorial by Jesse Berlin.
The longer answer, which is what I suspect you are really interested in, concerning criteria for minimum number of subjects for that study to be included in a traditional systematic review, is more complicated and debatable. Theoretically, sample size is taken into account in a traditional meta-anlaysis through inverse variance weighting of each study's results when included in a pooled analysis. This works fine for fixed effects analyses, but is problematic, in my opinion, in random effects analyses where the weights of studies are more equal and thus effects from smaller sized studies receive about as much weight as effects from larger sized studies. I suspect there is some literature on the question you have posed related to sample size being part of inclusion/exclusion criteria, but I have not seen it. Perhaps others have? cheers, fred
Some references for N-of-1 trials :
Zucker DR, Ruthazer R, Schmid CH. Individual (N-of-1) trials can be combined to give population comparative treatment effect estimates: methodologic considerations. J Clin Epidemiol. 2010 Dec;63(12):1312-23. [current methods paper]
Zucker DR, Ruthazer R, Schmid CH, Feuer JM, Fischer PA, Kieval RI, Mogavero N, Rapoport RJ, Selker HP, Stotsky SA, Winston E, Goldenberg DL. Lessons learned combining N-of-1 trials to assess fibromyalgia therapies. J Rheumatol. 2006 Oct;33(10):2069-77. [methods & example paper]
Zucker DR, Schmid CH, McIntosh MW, D'Agostino RB, Selker HP, Lau J. Combining single patient (N-of-1) trials to estimate population treatment effects and to evaluate individual patient responses to treatment. J Clin Epidemiol. 1997 Apr;50(4):401-10. [early methods paper]
Berlin JA. N-of-1 clinical trials should be incorporated into clinical practice. J Clin Epidemiol. 2010 Dec;63(12):1283-4. [editorial/commentary re: current methods paper]
Fredric M. Wolf, Ph.D., FACMI
Professor
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University of Washington
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From: "Baldassarre, Fulvia" <[log in to unmask]>
Subject: minimum number of subjects
Date: May 8, 2012 1:18:42 PM PDT
To: [log in to unmask]
Reply-To: "Baldassarre, Fulvia" <[log in to unmask]>
Hi All:
Has anyone seen any literature on setting a criteria for minimum number of subjects needed in a study for that study to be included in a systematic review?
Thanks
Fulvia
Fulvia Baldassarre, RN, MSc.
Research Coordinator
Program in Evidence-based Care, Cancer Care Ontario
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Hamilton, ON L8V 1C3
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