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The Use of the Number Needed to Treat (NNT) in Randomized Clinical Trials in Psychological Treatment


  • Cathy Shearer-Underhill,

  • Craig Marker

Address correspondence to Cathy Shearer-Underhill, Nova Southeastern University, Center for Psychological Studies, 3301 College Avenue, Fort Lauderdale, FL 33314. E-mail:


[Clin Psychol Sci Prac 17: 41–47, 2010]

There are many psychological treatments available for clinicians to implement with their clients, with numerous reports of which works best for whom. Clients have access to information regarding interventions and can benefit from easy-to-understand, yet powerful explanations of the results of treatment evaluations. The number needed to treat (NNT) is a potentially useful statistic, although it is highly underreported. A review of the Journal of Consulting and Clinical Psychology between 2000 and 2008 found that, of the 100 articles reviewed, four reported the NNT. Despite the need for powerful and intelligible statistics, behavioral scientists have yet to adopt and report the NNT in their results.

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