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trouble to develop a mathematical expression, called an
objective function, that expresses the values of
combinations of possible outcomes as a single measure
of cost-effectiveness, as is illustrated in Figure 4, even if
both cost and effectiveness must be described by more
than one measure. When achievement of the goals can
be quantitatively expressed by such an objective
function, designs can be compared in terms of their
value. Risks associated with design concepts can cause
these evaluations to be somewhat nebulous (because
they are uncertain and are best described by probability
distributions). In this illustration, the risks are relatively
high for design concept A. There is little risk in either
effectiveness or cost for concept B. while the risk of an
expensive failure is high for concept C, as is shown by the cloud of probability near the x axis with a high cost
and essentially no effectiveness. Schedule factors may
affect the effectiveness values, the cost values, and the
The mission success criteria for systems differ
significantly. In some cases, effectiveness goals may be
much more important than all others. Other projects
may demand low costs, have an immutable schedule, or
require minimization of some kinds of risks. Rarely (if
ever) is it possible to produce a combined quantitative
measure that relates all of the important factors, even if
it is expressed as a vector with several components.
Even when that can be done, it is essential that the
underlying factors and relationships be thoroughly
revealed to and understood by the system manager.
The system manager must weigh the importance of the
unquantifiable factors along with the quantitative data
provided by the system engineer.
Technical reviews of the data and analyses are
an important part of the decision support packages
prepared for the system manager. The decisions that
are made are generally entered into the configuration
management system as changes to (or elaborations of)
the system baseline. The supporting...
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