N of 1 trial

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An N of 1 trial is a clinical trial in which a single patient is the entire trial, a single case study. A trial in which random allocation can be used to determine the order in which an experimental and a control intervention are given to a patient is an N of 1 randomized controlled trial. The order of experimental and control interventions can also be fixed by the researcher.

This type of study has enabled practitioners to achieve experimental progress without the overwhelming work of designing a group comparison study. It can be very effective in confirming causality. This can be achieved in many ways. One of the most common procedures is the ABA withdrawal experimental design, where the patient problem is measured before a treatment is introduced (baseline) and then measured again during the treatment and finally when the treatment has terminated. If the problem vanished during the treatment it can be established that the treatment was effective. But the N=1 study can also be executed in an AB quasi experimental way; this means that causality cannot be definitively demonstrated. Another variation is non-concurrent experimental design where different points in time are compared with one another. This experimental design also has a problem with causality. But the replication of studies has a great value and can be as effective as a group study[citation needed]. The single case experimental design has been very effective in psychology and other field of behavior science[citation needed].

List of variation in N of 1 trial[edit]

Design Causality Use
A-B Quasi experiment Often the only possible method
A-A1-A Experiment Placebo design where A is no drug and A1 is a placebo
A-B-A Experiment Withdrawal design where effects of B phase can be established
A-B-A-B Experiment Withdrawal design where effects of B phase can be established
A-B-A-B-A-B Experiment Withdrawal design where effects of B phase can be established
A-B1-B2-B3-Bn-A Experiment Establishing the effect of different versions of B phase

Quasi experiment means that causality cannot be definitively demonstrated.
Experiment means that it can be demonstrated.


An N of 1 trial has been successfully to choose treatments whose optimal choice of treatment was uncertain for patients in diseases as diverse as osteoarthritis, chronic neuropathic pain and attention deficit hyperactivity disorder .[1]

See also[edit]


  1. ^ Scuffham PA, Nikles J, Mitchell GK, Yelland MJ, Vine N, Poulos CJ, Pillans PI, Bashford G, del Mar C, Schluter PJ, Glasziou P (2010). "Using N-of-1 trials to improve patient management and save costs". Journal of General Internal Medicine. 25 (9): 906–913. doi:10.1007/s11606-010-1352-7. PMC 2917656free to read. PMID 20386995. 
  • Guyatt GH, Keller JL, Jaeschke R, Rosenbloom D, Adachi JD, Newhouse MT (February 1990). "The n-of-1 randomized controlled trial: clinical usefulness. Our three-year experience". Ann. Intern. Med. 112 (4): 293–9. doi:10.7326/0003-4819-112-4-293. PMID 2297206. 
  • Johnston BC, Mills E (December 2004). "N-Of-1 Randomized Controlled Trials: An Opportunity for Complementary and Alternative Medicine Evaluation". J Altern Complement Med. 10 (6): 979–84. doi:10.1089/acm.2004.10.979. PMID 15673992. 
  • Avins AL, Bent S, Neuhaus JM (June 2005). "Use of an embedded N-of-1 trial to improve adherence and increase information from a clinical study". Contemporary Clinical Trials. 26 (3): 397–401. doi:10.1016/j.cct.2005.02.004. PMID 15911473. 
  • Nikles CJ, Mitchell GK, Del Mar CB, Clavarino A, McNairn N (June 2006). "An n-of-1 trial service in clinical practice: testing the effectiveness of stimulants for attention-deficit/hyperactivity disorder". Pediatrics. 117 (6): 2040–6. doi:10.1542/peds.2005-1328. PMID 16740846.