on medical decision analysis: Part 4—analyzing the model and interpreting the results. Med Decis Making. 1997;17:142–51. Updated Cost-of-Illness Model RESEARCH Vol. 41, No. 2 March/April 2001 Journal of the American Pharmaceutical Association 199 M E D I

This paper is the fourth of a five-part series that describes the principles of construction and evaluation of valid decision models. In this review, the authors describe the key principles of detecting and eliminating structural and programming errors in decision trees (debugging). In addition, they offer guidelines to facilitate the interpretation of analytic results of decision models. Key words: decision analysis; expected value; util-ity; sensitivity analysis; decision trees; probability. (Med Decis Making 1997;17:142-151) The first three parts of this seriesl-3 offer practical guidance in building a model that is structurally valid and clinically sensible, and obtaining the best available probabilities and utilities for the model. This paper is about the next step: evaluating the model and interpreting the results. &dquo;Folding back,&dquo; or analyzing the tree (described in detail in intro-ductory texts4’S) will give us the expected value fo