Analysis examine output

During the PHEA stage, the analyst has to identify likely human errors and possible ways of error detection and recovery. The PHEA prompts the analyst to examine the main performance-influencing factors (PIFs) (see Chapter 3) which can contribute to critical errors. All the task steps at the bottom level of the HTA are analyzed in turn to identify likely error modes, their potential for recovery, their safety or quality consequences, and the main performance-influencing factors (PIFs) which can give rise to these errors. In this case study, credible errors were found for the majority of the task steps and each error had multiple causes. An analysis of two operations from the HTA is presented to illustrate the outputs of the PHEA. Figure 7.12 shows a PHEA of the two following tasks Receive instructions to pump and Reset system. 

The best avenue is to use input data that would be considered the WCCE for the incident under evaluation. One should then question if the output data provided is realistic or corresponds to historical records of similar incidents for the industry and location. In other cases where additional analysis is needed, several release scenarios (small, medium and large) can be examined and probabilities can be assigned to each outcome. This would then essentially be an Event Tree exercise normally conducted during a quantitative risk analysis. Certain releases may also be considered so rare an event they may be outside the realm of accepted industry practical protective requirements. 

Another important reason for using multiple scenarios is to represent major sources of variability, or what-if scenarios to examine alternative assumptions about major uncertainties. This can be less unwieldy than including them in the model. Also, the distribution of outputs for each separate scenario will be narrower than when they are combined, which may aid interpretation and credibility. A special case of this occurs when it is desired to model the consequences of extreme or rare events or situations, for example, earthquakes. An example relevant to pesticides might be exposure of endangered species on migration. This use of multiple scenarios in ecological risk assessment has been termed scenario analysis, and is described in more detail in Ferenc and Foran (2000). 

The major benefit of 2nd-order Monte Carlo analysis is that it allows analysts to propagate their uncertainty about distribution parameters in a probabilistic analysis. An analyst need not specify a precise estimate for an uncertain parameter value simply because one is needed to conduct the simulation. The relative importance of our inability to precisely specify values for constants or distributions for random variables can be determined by examining the spread of distributions in the output. If the spread is too wide to promote effective decision making, then additional research is required. 

The results of the Monte Carlo analysis are stored in the output file. Examine the output file Select PSpice and then View Output File from the Capture menus. As you page down through the output file you will see a screen similar to the one shown below ... 

Cost-effectiveness and cost-benefit analyses are frequently mentioned in academic and policy-analysis circles. These notions center on careful examination of the costs and their corresponding outputs. Eisenberg defines cost-effectiveness analysis as the measure of the net cost of providing service (expenditures minus savings) as well as the results obtained (e.g., clinical results measured singly or a series of results measured on some scale). Cost-benefit analysis determines whether the cost is worth the benefits by measuring both in the same units. Such analyses will be critical, as future policy decisions are made with regard to the collection, allocation, and utilization of finite resources in the health care system for the enhancement of health status of the American people. 

In a simple sensitivity analysis, each parameter is varied individually, and the output is a qualitative understanding of which parameters have the most impact on project viability. In a more formal risk analysis, statistical methods are used to examine the effect of variation in all of the parameters simultaneously and hence quantitatively determine the range of variability in the economic criteria. This allows the design engineer to estimate the degree of confidence with which the chosen economic criterion can be said to exceed a given threshold. 

If dt and dx are always considered positive when increasing, you can use Eq. (6.1) without having any difficulties with signs. However, if you for some reason transfer an output to the left-hand side of the equation, or the equation is written in some other form, you should take great care in the use of signs (see Example 6.2 below). We are now going to examine some very simple unsteady-state problems which are susceptible to reasonably elementary mathematical analysis. You can (and will) find more complicated examples in texts dealing with all phases of mass transfer, heat transfer, and fluid dynamics. 

After an extensive analysis, Roberts concluded that most of the programs provided useful and comparable LC50 estimates. The exception to this was the UG-PROBIT. The commercially available packages in SAS and SPSSx had the advantages of graphical output and a method for dealing with control mortality. DULUTH-TOX and ASTM-TOX incorporated statistical tests to examine the data to assure that the assumptions of the probit calculations were met. 

Sht lamp eye examination may detect copper deposits in the eye (Kayser-Fleischer rings) and there may be abnormalities in liver frinction tests with an increased urine copper output (>500 fig Cu per L). Liver biopsy for copper analysis is useful in suspected cases and results above 250 fXg/g Cu dry weight are usually found (normal 8 to 40 Xg Cu per g dry weight). Failure of copper incorporation into plasma ceruloplasmin can also be demonstrated using an oral dose of stable Cu isotope. This may be helpful in excluding Wilson s disease when other tests are equivocal. Gene tracking and mutation detection are now possible, but since several hundred mutations exist this may not be informative. 

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