The weights used in computing the figure of merit can

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Unformatted text preview: biguously measured, and the appropriate level of effectiveness is known. Again, practical application requires that each of the alternatives be put on an equal effectiveness basis. This rule is dual to the one above in the following sense: For a given level of cost, the same alternative would be chosen by both rules; similarly, for a given level of effectiveness, the same alternative would be chosen by both rules. When it is not practical to equalize the cost or the effectiveness of competing alternatives, and cost caps or effectiveness floors do not rule out all alternatives save one, then it is necessary to form, either explicitly or implicitly, a cost-effectiveness objective function like the one shown in Figure 4 (Section 2.5). The cost-effectiveness objective function provides a single measure of worth for all combinations of cost and effectiveness. When this selection rule is applied, the alternative with the highest value of the cost-effectiveness objective function is chosen. Another group of selection rules is needed when cost and/or effectiveness cannot be represented as scalar quantities. To choose the best alternative, a multi-objective selection rule is needed. A multi-objective rule seeks to select the alternative that, in some sense, represents the best balance among competing objectives. To accomplish this, each alternative is measured (by some quantitative NASA Systems Engineering Handbook Systems Analysis and Modeling Issues method) in terms of how well it achieves each objective. For example, the objectives might be national prestige, upgrade or expansion potential, science data return, low cost, and potential for international partnerships. Each alternative's "scores" against the objectives are then combined in a value function to yield an overall figure of merit for the alternative. The way the scores are combined should reflect the decision maker's preference structure. The alternative that maximizes the value function (i.e., with the highest figure of merit) is then selected. In essence, this selection rule recasts a multi-objective decisi...
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