The fifth revised edition of this highly successful book presents the most extensive enhancement since Using and Understanding Medical Statistics was first published 30 years ago. Without question, the single greatest change has been the inclusion of source code, together with selected output, for the award-winning, open-source, statistical package kwn as R. This invation has enabled the authors to de-emphasize formulae and calculations, and let software do all of the 'heavy lifting'. This edition also introduces readers to several graphical statistical tools, such as Q-Q plots to check rmality, residual plots for multiple regression models, funnel plots to detect publication bias in a meta-analysis and Bland-Altman plots for assessing agreement in clinical measurements. New examples that better serve the expository goals have been added to a half-dozen chapters. In addition, there are new sections describing exact confidence bands for the Kaplan-Meier estimator, as well as negative bimial and zero-inflated Poisson regression models for over-dispersed count data. The end result is t only an excellent introduction to medical statistics, but also an invaluable reference for every discerning reader of medical research literature.