Assessing the economic impacts of alternative Information System (IS) designs and selecting IS design parameter values for a given decision setting are two important research issues in the domain of Information Systems. Evaluation studies based on information economics provide rigorous but restricted models, while traditional MIS studies suggest richer but less formal evaluation frameworks. ' In this paper, we attempt to combine the analytical rigor and descriptive richness into a unified and consistent basis for evaluating IS designs and making design modifications (improvements) to existing IS. Expanding on the concepts of information economics, a multi-dimensional mathematical model of information quality is developed. Several properties of the quality model with implications for system design are derived in the form of propositions. The impacts of information quality differential upon the effectiveness of an operational level decision setting are investigated through a decision-theoretic approach. Next, a hierarchical model is suggested for relating system design variables to the quality of information generated by the IS. Based on the quality differential impact analysis and the hierarchical model, a structured methodology for making design changes to existing IS is outlined.