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Unformatted text preview: uring design trade
studies may shift to a product view. This is not unlike the
progression of the cost modeling from simple
parametrics to more detailed grass-roots estimates.
The system engineer must tailor the effectiveness
measure and its measurement method to the resolution
Practical Pitfalls in Using Effectiveness Measures
in Trade Studies
Obtaining trustworthy relationships among the system
performance or technical attributes and system effectiveness is often difficult, Purported effectiveness mod els often only treat one or two of the facets described in
the text. Supporting models may not have been prop erly
integrated. Data are often incomplete or unreliable.
Under these conditions, reported system effectiveness
results for different alternatives in a trade study may
show only the relative effectiveness of the alternatives
within the context of the trade study. The system engineer must recognize the practical pitfalls of using such
results. NASA Systems Engineering Handbook
Systems Analysis and Modeling Issues
the system design. As the system design and
operational concept mature, effectiveness estimates
should mature as well. The system engineer must be
able to provide realistic estimates of system
effectiveness and its underlying performance and
technical attributes not only for trade studies, but for
project management through the tracking of TPMs.
This discussion so far has been predicated on
one accepted measure of system effectiveness. The job
of computing system effectiveness is considerably
easier when the system engineer has a single measure
and measurement method (model). But, as with costs, a
single measure may not be possible. When it does not
exist, the system engineer must fall back to computing
the critical high-level, but nevertheless still underlying,
system performance or technical attributes. In effect,
these high-level performance or technical attributes are
elevated to the status of measures of (system)
effectiveness (MoEs) for trade study purposes, even
though they do not represent a truly comprehensive
measure of system effecti...
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