Chemometric and statistical tools for data reduction and analysis abound, but the end objective of most analytical undertakings is to make informed decisions based on the data. Decision theory provides some highly instructive and intuitive tools to bridge the gap between data and optimal decisions. This tutorial provides a user-centric introduction to receiver operator characteristic curves, and related measures such as predictive values, likelihood ratios, and cost curves. Important considerations for choosing between these tools are discussed, as well as the primary methods for determining confidence intervals on the various measures. Numerous worked examples illustrate the calculations, their interpretation and potential drawbacks. (c) 2005 Elsevier B.V. All rights reserved.