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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
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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