Page 202 - Materials Chemistry, Second Edition

L1644_C05.fm Page 175 Monday, October 20, 2003 12:02 PM

The term simulation can be understood as an analytical method meant to imitate
a real-life system, especially when other analyses are too mathematically complex
or too difficult to reproduce. Without the aid of simulation, a spreadsheet model
would only reveal a single outcome, generally the most likely or average scenario.
Spreadsheet uncertainty analysis uses a spreadsheet model and simulation to analyze
the effect of varying inputs or outputs of the modeled system automatically. The
random behavior of how MC simulation selects variable values to simulate a model
is similar to that employed by games of chance. When a player rolls a die, he or
she knows that a 1, 2, 3, 4, 5, or 6 will come up, but does not know which will
occur in any particular roll. It is the same with the variables that have a known range
of values but an uncertain value for any particular time or event (Decisioneering
1996).

5.4.1 USE OF SOFTWARE PACKAGES TO PROPAGATE UNCERTAINTY
BY PERFORMING MONTE CARLO SIMULATION

In order to simplify the task of determining the uncertainty of a parameter by MC
simulation, various commercial software packages are available. Among them, Crys-
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tal Ball ,* @Risk ,** Analytica,*** Stella II ,**** PRISM ***** and Susa-
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PC ****** can be highlighted. Table 5.1 summarizes the main information about
each of these software packages.
According to Metzger et al. (1998), @Risk was originally designed for business
applications, but it has found wide use in human health and ecological risk assess-
ment. This package includes uncertainty in estimates to generate results that show
all possible outcomes. Because of its standardized spreadsheet backbone, @Risk is
easy to use without a need for extensive statistical knowledge, modeling capability
or programming ability.
Analytica and Stella II are two stand-alone programs designed for a wide variety
of applications. Analytica is a model-building program that attempts to simplify
sophisticated systems with the use of multilevel influence diagrams. Stella II is a
multilevel hierarchical environment for constructing and interacting with models.
These two programs are designed to simplify complex problems and therefore
require additional effort in learning the software and building the models. However,
because these models are displayed in diagrams, their interpretation for other users
tends to be easier than for any other software package.
PRISM and Susa-PC are Fortran-based codes, designed specifically for use in
risk analysis. PRISM is a simple free-access program that builds distributions for
input into any model and then analyzes the output of that model. Susa-PC is a more

* Registered trademark of Decisioneering, Inc., Denver, CO.
** Registered trademark by Palisade Corporation, Newfield, NY.
*** Registered trademark of Decisioneering, Inc., Denver, CO.
**** Registered trademark of High Performance Systems, Inc., Lebanon, NH.
***** Registered trademark of SENES Oak Ridge, Inc., Oak Ridge, TN.
****** Registered trademark of Gesellschaft für Anlagenund Reaktorsicherheit (GRS) mbH, Köln,
Deutschland.

© 2004 CRC Press LLC