Prescriptive Approach

In the previous section we described several internal methods of quality assessment that provide quantitative estimates of the systematic and random errors present in an analytical system. Now we turn our attention to how this numerical information is incorporated into the written directives of a complete quality assurance program. Two approaches to developing quality assurance programs have been described a prescriptive approach, in which an exact method of quality assessment is prescribed and a performance-based approach, in which any form of quality assessment is acceptable, provided that an acceptable level of statistical control can be demonstrated. 

With a prescriptive approach to quality assessment, duplicate samples, blanks, standards, and spike recoveries are measured following a specific protocol. The result for each analysis is then compared with a single predetermined limit. If this limit is exceeded, an appropriate corrective action is taken. Prescriptive approaches to quality assurance are common for programs and laboratories subject to federal regulation. For example, the Food and Drug Administration (FDA) specifies quality assurance practices that must be followed by laboratories analyzing products regulated by the FDA. 

The first sample to be analyzed is the field blank. If its spike recovery is unacceptable, indicating that a systematic error is present, then a laboratory method blank. Dp, is prepared and analyzed. If the spike recovery for the method blank is also unsatisfactory, then the systematic error originated in the laboratory. An acceptable spike recovery for the method blank, however, indicates that the systematic error occurred in the field or during transport to the laboratory. Systematic errors in the laboratory can be corrected, and the analysis continued. Any systematic errors occurring in the field, however, cast uncertainty on the quality of the samples, making it necessary to collect new samples. 

If the field blank is satisfactory, then sample B is analyzed. If the result for B is above the method s detection limit, or if it is within the range of 0.1 to 10 times the amount of analyte spiked into Bsf, then a spike recovery for Bsf is determined. An 

Example of a prescriptive approach to quality assurance. Adapted from Environmental Monitoring and Support Laboratory, U.S. Environmental Protection Agency, Handbook for Analytical Quality Control in Water and Wastewater Laboratories, March 1979. 

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A good example of a prescriptive approach to quality assessment is the protocol outlined in Figure 15.2, published by the Environmental Protection Agency (EPA) for laboratories involved in monitoring studies of water and wastewater. Independent samples A and B are collected simultaneously at the sample site. Sample A is split into two equal-volume samples, and labeled Ai and A2. Sample B is also split into two equal-volume samples, one of which, Bsf, is spiked with a known amount of analyte. A field blank. Dp, also is spiked with the same amount of analyte. All five samples (Ai, A2, B, Bsf, and Dp) are preserved if necessary and transported to the laboratory for analysis. 

Once a control chart is in use, new quality assessment data should be added at a rate sufficient to ensure that the system remains in statistical control. As with prescriptive approaches to quality assurance, when a quality assessment sample is found to be out of statistical control, all samples analyzed since the last successful verification of statistical control must be reanalyzed. The advantage of a performance-based approach to quality assurance is that a laboratory may use its experience, guided by control charts, to determine the frequency for collecting quality assessment samples. When the system is stable, quality assessment samples can be acquired less frequently. 

Although this approach enables companies to comply with legislation, and harmful emissions will be prevented from entering the environment, it does not provide the best framework for sustainable development. A much better approach would be to develop legislation that encourages pollution prevention at source. In this respect, the old prescriptive approach has something to offer however, it is generally accepted that with the number of diverse operations we have today this would be unworkable. 

Unlike the procedure followed in developing logic trees, the investigation team does not construct the tree. Rather they apply each causal factor to each branch of the predefined tree in turn, and those branches that are not relevant to the incident are discarded. This prescriptive approach offers consistency and repeatability by presenting different investigators with the same standard set of possible root causes for each incident. 

These studies can use data from various sources available within (internal) and from outside (external) a specific health care organization. Common approaches to modeling are to modify and adapt existing models or to develop a distinct model to answer a specific question. Typically, economic modeling in today s practice settings employs clinical decision analysis, which has been defined as an explicit, quantitative, and prescriptive approach to choosing among... 

Prescriptive approaches for group decision making, 2212-2214 Presentation language, 131-132 Presentation support software, 142 Present worth, probability distribution for, 2367-2369, 2371-2376 discrete distribution, 2372-2373 expected present worth, 2367-2368 mean and variance, using only, 2373-2374 normal distribution, assumption of, 2374-2376... 

A similar but opposite assumption is also in play with the prescriptive approach. The presence of a criterion may imply that the characteristic in question is the only means by which the system can be rendered safe . Continuing the HL7 example above, there is the assumption that the use of any other communication standard would be intrinsically associated with intolerable risk. Clearly this logic does not follow. A system may use a perfectly reliable vendor-specific message format, one that the manufacturer has utilised for many years and has a great deal of operational experience with. Indeed a change in technology to meet the requirements of the... 

Unlike the prescriptive approach, the goal-based methodology enables an assessment and re-assessment of risk as operational experience is gained. The intelligence gathered after system go-live provides powerful lessons from which the safety position can be re-evaluated and further evidenced. A simple prescriptive checklist fails to take these important messages into account. 

Goal-based methods are preferable to prescriptive approaches. They allow risk to be objectively justified and explained in the form of a safety case. 

Breslin, P. (2004). Performance versus prescriptive approaches to OHS in the Victorian construction industry. JoMiTM / of Occupational Health and Safety-Australia and New Zealand, 20(6), 563-571. 

The MMS s Safety and Environmental Management Program (SEMP) was developed in response to the 1990 finding of the National Research Council s Marine Board that MMS s prescriptive approach to regulating offshore operations had forced industry into a compliance mentality. The Marine Board found further that this compliance mentality was not conducive to effectively identify all the potential operational risks or developing comprehensive accident mitigation. As a result, the Marine Board recommended and MMS concurred that a more systematic approach to managing offshore operations was needed. 

The first safety cases prepared for the process industries were those developed for North Sea offshore oil and gas operations following the Piper Alpha disaster that occurred in the year 1988. The Cullen report (Cullen, 1990) that was written following that accident was highly critical of offshore operating practices and recommended that a safety case approach be implemented. The Seveso incident that occurred in Italy further prompted the increased use of safety cases. Since that time the use of safety cases has spread to other industries (such as mining and railway operations) and to other nations, primarily in Europe and Australasia. (It is notable that the safety case regime approach has not been taken up for offshore oil and gas operations in the Gulf of Mexico—instead a more prescriptive approach based on industry consensus standards is used.)... 

There are many limitations of the prescriptive approach to safety, of which some are discussed in more detail in Chapter 7 and several other chapters. Here we point at the following ... 

As if problems such as these were not enough to call into question the wisdom of the detailed prescriptive approach which had been requested by the Sea Gem Inquiry and enthusiastically endorsed by Parliament, there is in fact one more issue that appears to hammer a final nail into the coffin. Recognising that health and safety at work was a general problem in all industries, a government-sponsored inquiry had been established under the chairmanship of Lord Robens to consider the matter in its entirety. Reporting in 1972, after the passing of the Mineral Workings (Offshore Installations) Act but before it had entered into force, the... 

These regulations illustrate a trend that is occurring in safety legislation, which is now starting to move from a prescriptive approach with definitions of what has to be done in specific situations to a more risk-based approach where the precautions and actions taken are left to the individual user provided they meet certain risk-based criteria. A proposed European Directive concerning minimum requirements for improving the safety and health of workers potentially at risk from explosive atmospheres extends this concept to all work places where flammable atmospheres may be formed. When adopted, this will require all employers to carry out a hazard assessment to identify whether a flammable atmosphere is likely to exist and, where so, to demonstrate that appropriate technical, organisational and other measures appropriate to the nature of the operation have been taken to minimise the risk. 

An implication of these criteria is that research that takes a purely descriptive (e.g., empirical research that seeks to validate certain hypothesized relationships) rather than prescriptive approach will not be subject to our detailed review, although we will briefly mention some such works. 

To a great extent, laws, regulations, and standards drive safety and health practices in the United States. It is a prescriptive approach. Standards and regulations prescribe how to achieve safety, and enforcement focuses on compliance with the standards and regulations. 

Explain the basic difference between a prescriptive approach to safety and health regulation and a performance approach. 

Most national fire safety strategies are based on prescriptive approaches that have been developed historically to meet fire safety needs, often in the wake of major fire disasters. Building regulations of most countries have codes that can be stated in very general terms, as seeking to insure that [111] ... 

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