Confidence intervals rather than P values: Estimation rather than hypothesis testing

Abstract

Overemphasis on hypothesis testing—and the use of P values* to dichotomise significant or non-significant results—has detracted from more useful approaches to interpreting study results, such as estimation and confidence intervals. In medical studies investigators are usually interested in determining the size of difference of a measured outcome between groups, rather than a simple indication of whether or not it is statistically significant. Confidence intervals present a range of values, on the basis of the sample data, in which the population value for such a difference may lie. Some methods of calculating confidence intervals for means and differences between means are given, with similar information for proportions. The paper also gives suggestions for graphical display. Confidence intervals, if appropriate to the type of study, should be used for major findings in both the main text of a paper and its abstract. © 1986, British Medical Journal Publishing Group. All rights reserved.