This paper derives a general prescriptive model for group decision analysis based on a set of logical and operational assumptions analogous to those for individual decision analysis. The approach accounts for each group member's potentially different frames of their common decision, including different events and different consequences of concern. Assuming that each group member accepts the decision analysis assumptions to evaluate his or her analysis of what the group should do and that the group accepts an analogous set of decision analysis assumptions for the group's decision, it is proven that the group expected utility for an alternative should be a weighted sum of the individual member's expected utilities for the alternatives. After each group member does his or her decision analysis of the group's alternatives, the essence of the group decision analysis is to specify the weights based on the interpersonal comparison of utilities and on the relative importance or power of each individual in the group.