文档介绍：Review
Synthèse
Tips for learners of evidence-based medicine:
2. Measures of precision (confidence intervals)
Victor M. Montori, Jennifer Kleinbart, Thomas B. Newman, Sheri Keitz, Peter C. Wyer,
Virginia Moyer, Gordon Guyatt, for the Evidence-Based Medicine Teaching Tips Working Group
n the first article in this series,1 we presented an ap- these concepts to clinicians, is available online at www.
proach to understanding how to estimate a treatment’s .
I effectiveness that covered relative risk reduction, ab-
solute risk reduction and number needed to treat. But how Clinician learners’ objectives
precise are these estimates of treatment effect?
In reading the results of clinical trials, clinicians often Making confidence intervals intuitive
come across 2 related but different statistical measures of an
estimate’s precision: p values and confidence intervals. The p • Understand the dynamic relation between confidence
value describes how often apparent differences in treatment intervals and sample size.
effect that are as large as or larger than those observed in a
particular trial will occur in a long run of identical trials if in Interpreting confidence intervals
fact no true effect exists. If the observed differences are suf-
ficiently unlikely to occur by chance alone, investigators re- • Understand