Decision analytic modeling (DAM) has been increasingly used within the past 30 years to synthesize clinical and economic evidence and support both clinical and policy-level decision making. Decision models often represent complex decision and synthesize data from a variety of sources, and they may be difficult to validate and interpret. Thus, while DAM can be extremely useful, it is also difficult to do well. Errors are common among neophytes and not uncommon even in published decision analyses. This entry reviews the steps associated with constructing a decision model and describes several of the most common errors in model construction, analysis, and interpretation. It considers both conceptual errors in [Page 263]model construction and errors of computation or calculation. Although DAM is commonly used in economic evaluation, ...