Qualitative assessment, description

Mechanistic Approaches. Adequate and appropriate river-quality assessment must provide predictive information on the possible consequences of water and land development. This requires an understanding of the relevant cause and effect relationships and suitable data to develop predictive models for basin management. This understanding may be achieved through qualitative, semi-quantitative or quantitative approaches. When quantitative or semi-quantitative methods are not available the qualitative approach must be applied. Qualitative assessments involve knowledge of how basin activities may affect river quality. This requires the use of various descriptive methods. An example of this kind of assessment is laboratory evaluation of the extent to which increases in plant nutrients, temperature or flow may lead to accelerated eutrophication with consequent reduction of water quality. 

The relative effect of the uncertainties above on the performance of the mathematical model depends on the system but the uncertainty in the conceptual model dominates in many cases. The effect of parameter uncertainty and variability depends on the system, and is to some extent possible to quantify by sensitivity and imcertainty analysis. However, uncertainty in the conceptual model is difficult to assess. A qualitative systematic description of the physical and chemical processes, their importance and interactions, and boundary conditions is necessary in order to minimize the uncertainty in the conceptual model. 

All interactions are documented in a database using special protocols, including a detailed description of the process including cause and effects, qualitative assessment of its importance and literature references. In this study the description of the diagonal and interaction elements are made in a less formal way. 

Hazard information is converted to risk information by evaluating the severity of potential accidents associated with the hazard and by evaluating the probability that the hazard could produce an accident. It is done by developing a matrix with severity on one axis and probability on the other, with a numeric code used to represent the risk associated with each hazard. This risk assessment code (RAC) is used to prioritize hazards and determine their acceptability. Hazard severity may be expressed quantitatively (for example, dollar loss or number of injuries), qualitatively (verbal descriptions), or as a combination (Table 11-1). 

Each technology description is followed by tables representing the qualitative assessment of individual conunittee members assigned to investigate that technology based on their expertise. The committee took these qualitative assessments into account in its overall ranking of technologies. 

Description of QRA analysis case study A hazard and operability study was used to identify hazardous scenarios arising from the process. These were qualitatively assessed and a risk ranking was established. With knowledge of the operational procedures and intended layout of the plant, the key potential accidents identified in the HAZOP have been rationalised for the purposes of the case study to ... 

Furthermore, there often is a form of evidential uncertainty for the assessor in relation to evidential propositions. Finally, it is possible that the assessor has accepted data, models or judgments the justification of which is (partly) based on values. Hence, the justification may not only of Epistemic nature (Ej), but also may involve of Non-Epistemic nature (NEJ). Hence, the risk description is not necessarily value-free, depending on the nature of the reasons because of which a particular propositional attitude is adopted regarding the evidences. A qualitative assessment of evidential biases can make such value-laden considerations explicit. 

At the end of the test, the container is opened, and the test specimens are inspected and evaluated. While the evaluation may involve quantitative measurements (such as weight loss due to pieces being broken off or abraded away, or the change in measured value of a specific performance parameter), qualitative assessments are often more valuable. Qualitative assessments may include a description of common failure modes, observations of high wear areas, and commentary on overall performance. 

The uncertainties in human error rates may be within the stated uncertainty bounds, but such is not demonstrated from sparse experiments. Both the qualitative description of the human interaction logic and the quantitative assessment of those actions rely on the virtually untested judgment of experts. 

Because most research effort in the human reliability domain has focused on the quantification of error probabilities, a large number of techniques exist. However, a relatively small number of these techniques have actually been applied in practical risk assessments, and even fewer have been used in the CPI. For this reason, in this section only three techniques will be described in detail. More extensive reviews are available from other sources (e.g., Kirwan et al., 1988 Kirwan, 1990 Meister, 1984). Following a brief description of each technique, a case study will be provided to illustrate the application of the technique in practice. As emphasized in the early part of this chapter, quantification has to be preceded by a rigorous qualitative analysis in order to ensure that all errors with significant consequences are identified. If the qualitative analysis is incomplete, then quanhfication will be inaccurate. It is also important to be aware of the limitations of the accuracy of the data generally available... 

Hazard characterization (or dose-response assessment) is the qualitative and, as far as possible, quantitative description of the inherent properties of an agent or situation having the potential to cause adverse effects. This step should include a dose-response assessment that describes the severity of adverse effects (the responses) related to the amount and condition of exposure to an agent (the dose). 

The assessment endpoint should be not only measurable (at least potentially) but also modelable. Defining a modelable endpoint is likely to require close discussion between an assessor (who knows what they can model) and a risk manager (who knows what they want to protect). Sometimes the assessment endpoint is only indirectly related to the management goal, for example, if the assessment endpoint is a risk to individuals, but the aim is to protect population sustainability. In such cases, qualitative inference will be required to interpret the assessment result. This inference will need to be done jointly by the risk assessor and risk manager. It is likely to involve substantial uncertainty, which will have to be taken into account qualitatively when producing a narrative description of the assessment outcome. This step should be identified as part of the conceptual model. 

The use of statistical tests to analyze and quantify the significance of sample data is widespread in the study of biological systems where precise physical models are not readily available. Statistical tests are used in conjunction with measured data as an aid to understanding the significance of a result. Their aid in data analysis fills a need to answer the question of whether or not the inferences drawn from the data set are probable and statistically relevant. The statistical tests go further than a mere qualitative description of relevance. They are designed to provide a quantitative number for the probability that the stated hypothesis about the data is either true or false. In addition, they allow for the assessment of whether there are enough data to make a reasonable assumption about the system. 

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