By supplying pert with the minimum maximum and most

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Unformatted text preview: perceptions, not necessarily objective risk as defined by the above equation. Perceptions of consequences tend to grow faster than the consequences themselves—that is, several small accidents are not perceived as strongly as one large one, even if fatalities are identical. There are difficulties in dealing with incommensurables, as for example, lives vs. dollars. mathematics of these trees is similar to that for decision trees. The consequences of each accident sequence are generally measured both in terms of direct economic losses and in public health effects. (See sidebar on PRA pitfalls.) Doing a PRA is itself a major effort, requiring a number of specialized skills other than those provided by reliability engineers and human factors engineers. PRAs also require large amounts of system design data at the component level, and operational procedures data. For additional information on PRAs, the system engineer can reference the PRA Procedures Guide (1983) by the American Nuclear Society and Institute of Electrical and Electronic Engineers (IEEE). Probabilistic Network Schedules. Probabilistic network schedules, such as PERT (Program Evaluation and Review Technique), permit the duration of each activity to be treated as a random variable. By supplying PERT with the minimum, maximum, and most likely duration for each activity, a probability distribution can be computed for project completion time. This can then be used to determine, for example, the chances that a project (or any set of tasks in the network) will be completed by a given date. In this probabilistic setting, however, a unique critical path may not exist. Some practitioners have also cited difficulties in obtaining meaningful input data for probabilistic network schedules. A simpler alternative to a full probabilistic network schedule is to perform a Monte Carlo simulation of activity durations along the project's critical path. (See Section 5.4.2.) Probabilistic Cost and Effectiveness Models. These models offer a probabilistic view of a project's cost and effectiveness outcome...
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This document was uploaded on 02/26/2014 for the course E 515 at University of Louisiana at Lafayette.

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