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Unformatted text preview: ility not possessed by SIMSYLS.
For more detail, see DeJulio, E., SIMSYLS User's Guide, Boeing Aerospace Operations, February 1990, and Kline,
Robert, et al., The MSPARE Model, LMI, NS901R1, March 1990. cies. (See Section 6.5 for more on Integrated Logistics
Support.)
5.4 Probabilistic Treatment of Cost and
Effectiveness A probabilistic treatment of cost and
effectiveness is needed when point estimates for these
outcome variables do not "tell the whole story"—that is,
when information about the variability in a system's projected cost and effectiveness is relevant to making
the right choices about that system. When these
uncertainties have the potential to drive a decision, the
systems or program analyst must do more than just
acknowledge that they exist. Some useful techniques for
modeling the effects of uncertainty are described below
in Section 5.4.2. These techniques can be applied to
both cost models and effectiveness models, though the
majority of examples given are for cost models. NASA Systems Engineering Handbook
Systems Analysis and Modeling Issues
5.4.1 Sources of Uncertainty in Models There are a number a sources of uncertainty in
the kinds of models used in systems analysis. Briefly,
these are:
• • • Uncertainty about the correctness of the model's
structural equations, in particular whether the
functional form chosen by the modeler is the
best representation of the relationship between
an equation's inputs and output
Uncertainty in model parameters, which are, in
a very real sense, also chosen by the modeler;
this uncertainty is evident for model coefficients
derived from statistical regression, but even
known physical constants are subject to some
uncertainty
due
to
experimental
or
measurement error
Uncertainty in the true value of model inputs
(e.g., estimated weight or thermal properties)
that describe a new system. As an example, consider a cost model
consisting of one or more statistical CERs. In the early
phases of the project life cycle (Ph...
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This document was uploaded on 02/26/2014 for the course E 515 at University of Louisiana at Lafayette.
 Spring '13
 Mr.Kau
 Systems Engineering, The American

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