Indian Journal of Urology Users online:882  
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Year : 2011  |  Volume : 27  |  Issue : 4  |  Page : 532-535

Understanding results: P-values, confidence intervals, and number need to treat

1 Department of Urology, University of California, San Francisco, CA, USA
2 Department of Urology, University of Texas Health Science Center at San Antonio, San Antonio, TX, USA

Correspondence Address:
Timothy Y Tseng
Department of Urology, University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, Mail Code 7845 San Antonio, TX 78229
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0970-1591.91447

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Objectives: With the increasing emphasis on evidence-based medicine, the urology literature has seen a rapid growth in the number of high-quality randomized controlled trials along with increased statistical rigor in the reporting of study results. P-values, CI, and number needed to treat (NNT) are becoming increasingly common in the literature. This paper seeks to familiarize the reader with statistical measures commonly used in the evidence-based literature. Materials and Methods: The meaning and appropriate interpretation of these statistical measures is reviewed through the use of a clinical scenario. Results: The reader will be better able to understand such statistical measures and apply them to the critical appraisal of the literature. Conclusions: P-values, CI, and NNT each provide a slightly different estimate of statistical truth. Together, they provide a more complete picture of the true effect observed in a study. An understanding of these measures is essential to the critical appraisal of study results in evidence-based medicine.

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