Expert judgment

Four general classes of HRA methods irc. (I) expert judgment, (2) performance process simulation, (3) performance data analysis, and (4) dependency calculations, ri.ese classes rue encompassed in the ten methods many of which contain multiple dassc.s of the methods. No attempt is made to dassity them according to the methods. 

The paired comparisons method (NUREG/CR-3688) is a structured expert judgment method in which human errors are compared in pairs. By combining the judgments of the group of experts, the errors arc arranged in order of likelihood of occurrence, of the human errors considered, they can be used as "anchor points list. Documentation requirements are given in Table 4.5-8. 

Embry, D. E. et al., SLIM-MAUD an Approach to Assessing Human Error Probabihues Using Structured Expert Judgment, BNL, March 1984. 

Comer, M. K. et al, enerating Human Reliability Estimates using Expert Judgment. SNL, November 1984. 

Wheeler, T. A. et al., Analysis of Core Damage Frequency from Internal Events Expert Judgment Elicitation, Vol. 2. 1989... 

Remember also to take advantage of the team s individual, anecdotal experience with your company s management systems. Defining your company s management systems approach will be greatly enhanced by drawing on expert judgment as well as quantitative methods. 

The SLIM technique is a highly flexible method that allows considerable freedom in performing what-if analyses. In common with most human reliability quantification techniques, it requires defensible data, preferably from a plant environment, to be effective. In the absence of such data, the calibration values have to be generated by expert judgments made by experienced plant personnel. 

Embrey, D. E., Kirwan, B., Rea, K., Humphreys, P., Rosa, E. A. (1984). SLIM-MAUD. An approach to Assessing Human Error Probabilities Using Structured Expert judgment Vols. I and II. Washington, DC NUREG/CR—3518 US Nuclear Regulatory Commission. 

Failure rates from published sources or expert judgment... 

Expert Judgment quantifies an expert s state of knowledge or perceptions of the likelihood of an incident. This knowledge may be based on historical data, insights gained from models, experience, or a combination of these factors. 

Data may be inaccurate, incomplete, or inappropriate Data from related activities might not be directly applicable Data generated by expert Judgment may be inaccurate Improper or incomplete chmacterization of the general population... 

Cause-consequence analysis serx es to characterize tlie physical effects resulting from a specific incident and the impact of these physical effects on people, the environment, and property. Some consequence models or equations used to estimate tlie potential for damage or injury are as follows Source Models, Dispersion Models, Fire Explosion Models, and Effect Models. Likelihood estimation (frequency estimation), cliaractcrizcs the probability of occurrence for each potential incident considered in tlie analysis. The major tools used for likelihood estimation are as follows Historical Data, Failure sequence modeling techniques, and Expert Judgment. 

ECVAM as part of the JRC fulfills the task to validate alternative methods. Its advisory group ES AC advises ECVAM scientifically and gives expert judgment on the different proposed non-animal tests. 

There are two approaches that may be taken in integrating all of these factors. The first is a full calculation of the hazard from fires. This calculation requires the use of a computer and a sizable amount of expert judgment. The second approach involves a derived index. This is generally an algebraic combination of a few pieces of data leading to a value indicative of relative fire safety. An example of each approach is provided below. 

These criteria and methods are based on a combination of results from animal experiments, observations of long- and short-term human exposures, and expert judgment. The following paragraphs define these criteria and describe some of their features. 

In the authors opinion, even if imperfect, the CLL approach is preferable to apply for ecosystem risk assessment than a qualitative EcoRA based mainly on expert judgment. 

Catalytic Point Detection Moderate Moderate ISA CSA (API) Easily Positioned Industry Standard Detection Device Poisoning Limited to Spot Detection Costly Maintenance Expert Judgment Required for Placement Point Sources (Pumps, Compressors, Seals, etc.)... 

An adaptation, where an organism stabilizes its physiological condition after exposure to a chemical, without any irreversible disruption of a biological system and without exceeding the normal capacities of its response, should be considered as an early, not yet adverse, effect, which later on might lead to an adverse effect and thus needs expert judgment in a case-by-case manner. 

If there are several valid studies addressing the same effect from which different NOAELs could be derived, the highest reliable NOAEL not exceeding any of the reliable LOAELs should be used in the hazard assessment. If the smdies are not quite comparable, i.e., do not examine the same endpoints by equally sensitive methods, expert judgment is used to derive the most relevant NOAEL. When it is not possible to derive a NOAEL, the LOAEL should be used in the hazard assessment. 

If a single adequate study demonstrates no carcinogenic effects, expert judgment is needed to decide on whether a second study is needed to further support the noncarcinogenicity of the substance, based on all available data in addition to the carcinogenicity study. 

Probabilistic methods can be applied in dose-response assessment when there is an understanding of the important parameters and their relationships, such as identification of the key determinants of human variation (e.g., metabolic polymorphisms, hormone levels, and cell replication rates), observation of the distributions of these variables, and valid models for combining these variables. With appropriate data and expert judgment, formal approaches to probabilistic risk assessment can be applied to provide insight into the overall extent and dominant sources of human variation and uncertainty. 

In 1990, Lewis et al. published a new approach introducing flexibility such that both new information and expert judgment could be readily incorporated. The Lewis-Lynch-Nikiforov (LLN) method, and its rehnements, are extensions of established principles and procedures, and... 

UFm accounts for the quality and relevance of the database, i.e., accounts for the uncertainties in the establishment of a NOAEL for the critical effect. The UFm includes elements such as (1) the quality of the database, e.g., data on specific toxic endpoints are lacking or inadequate, default value of 1-10 (2) route-to-route extrapolation, e.g., no studies using the appropriate exposure route are available, no default value (3) LOAEL-to-NOAEL extrapolation, e.g., a NOAEL cannot be established for the critical effect, default value of 10 (4) subchronic-to-chronic extrapolation, e.g., no chronic studies on which to establish the NOAEL are available, default value of 10 and (5) nature and severity of toxicity, e.g., the critical effect is toxicity to reproduction, carcinogenicity or sensitization, default value of up to 10. A default value for UFm has not been recommended however, a value from 1 to 100 is generally used. The value is evaluated case-by-case based on expert judgment. 

Vermeire et al. (1999) noted that for both extrapolations, the results were hardly influenced by the assumptions made on absorption, indicating that other factors may be important in route-to-route extrapolation and/or the reliability of the estimates of absorption used in the study was poor. Vermeire et al. (1999) also concluded that scientific justification for the application of route-to-route extrapolation was not derived in this smdy and heavily depends on expert judgment. 

KEMI (2003) noted that route-to-route extrapolation can only be performed in the case of systemic toxicity and that possible local toxicity in the airways cannot be detected. Not only the degree of absorption but also metabolism should be considered, as, e.g., compounds may be highly metabolized in the liver due to first-pass effect in case of oral exposure but much less metabolized in the case of other routes of exposure. KEMI also noted that there are databased distributions of NOAEL ratios from different routes of exposure, but the size and reliability of this database are limited and they therefore suggested that these distributions should not be used. KEMI suggested that kinetic data are required if possible and that route-to-route extrapolation should be performed in a case-by-case manner based on expert judgment of scientific information. In case no data are available to base the extrapolation upon, 100% should be used as the default degree of absorption. It was emphasized that this default level is generally very conservative in the case of dermal exposure, while in case of inhalation exposure, this default level may not be conservative at all and may even be the opposite. 

No default factor has been suggested for route-to-route extrapolation. It is generally recommended that whether an extrapolation of data is justified in a given situation should be decided on a case-by-case basis, based on expert judgment of scientific information. 

In conclusion, the assessment factor for route-to-route extrapolation should preferentially be described probabilistically however, at present there is no valid and reliable database-derived distribution. No default factor can be suggested for route-to-route extrapolation. Whether a route-to-route extrapolation is justified in a given situation should be decided on a case-by-case basis, based on expert judgment of scientific information, and should generally not be undertaken in cases where no information is available on the other route. 

Vermeire et al. (1999) pointed out that there is no scientific basis for any value of a default factor to account for uncertainty in the NOAEL, nor any distribution. The authors considered the use of LOAEL/NOAEL ratios to estimate a NOAEL from a LOAEL as questionable, since doses in toxicological tests are usually spaced at fixed intervals and the observed distribution of LOAEL/NOAEL ratios primarily reflects the historical frequency of use of various dose spacing. There is no guarantee whatsoever that extrapolation of a LOAEL with any factor will yield an estimate of the NOAEL. Therefore, this factor can only be assigned using expert judgment in which... 

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