When it is not practical to equalize the cost or the

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Unformatted text preview: he former class, the measures of system effectiveness, performance or tech - NASA Systems Engineering Handbook Systems Analysis and Modeling Issues or output, or the number of platforms or instruments, may suffice. In other types of trade studies, this may not be possible. nical attributes, and system cost for the alternatives in the trade study look like those for alternative B. In the latter class, they look like those for alternative C. When they look like those for alternative A, conditions of uncertainty should apply, but often are not treated that way. The table further divides each of the above classes of decision problems into two further categories: those that apply when cost and effectiveness measures are scalar quantities, and thus suffice to guide the system engineer to the best alternative, and those that apply when cost and effectiveness cannot be represented as scalar quantities. Selection Rules When Uncertainty Is Subordinate, or Not Considered. Selecting the alternative that maximizes net benefits (benefits minus costs) is the rule used in most cost-benefit analyses. Cost-benefit analysis applies, however, only when the return on a project can be measured in the same units as the costs, as, for example, in its classical application of evaluating water resource projects. Another selection rule is to choose the alternative that maximizes effectiveness for a given level of cost. This rule is applicable when system effectiveness and system cost can be unambiguously measured, and the appropriate level of cost is known. Since the purpose of the selection rule is to compare and rank the alternatives, practical application requires that each of the alternatives be placed on an equal cost basis. For certain types of trade studies, this does not present a problem. For example, changing system size A related selection rule is to choose the alternative that minimizes cost for a given level of effectiveness. This rule presupposes that system effectiveness and system cost can be unam...
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This document was uploaded on 02/26/2014 for the course E 515 at University of Louisiana at Lafayette.

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