Demos is a modeling environment designed to help a co-operating team design, analyze, critique and refine quantitative models for policy research. Earlier research found that readers of Demos models tended to become disoriented while exploring models online. In response we have designed and implemented a graphical interface to Demos named Demaps. Demaps displays diagrams of the model structure, both dependence networks and abstraction hierarchies, to provide graphic context and direct manipulation style of interaction. We describe a study of the use of Demaps to understand and compare multiple versions of models. The study employs verbal protocol analysis to evaluate the design of Demaps and to discover expert strategies for model understanding and criticism. Subjects were able to learn to use Demaps effectively in about an hour to review and compare policy models and perform sensitivity analyses. The study describes two strategies used in reading models and suggests the desirability of additional facilities for recording model critiques and accessing detailed background information on models.

*We gratefully acknowledge the contributions of many people, including Jill Larkin, Jim Morris, Granger Morgan, Andrew Appel. and our subjects. This work was supported by the Information Technology Center and the National Science Foundation under grant IST-8316890.