Retrospective approach

After the initial inventory reporting cutoff in May of 1978, this retrospective approach was replaced with the flow of current information. New substances, as they became commercial, had to be identified and put through a decision process as shown in Figure 2. New reports were again necessitated by the commercialization of a new substance. Since July of 1979. Section 5 Compliance has been the source of nearly all compliance activity. Input for Premanufacture Notification purposes now takes a shape similar to that previously indicated, (see Figure 2) but now incoming new product material must reach the coordinator earlier in the life of the product than at any other time in the compliance effort. This introduced a potential time delay in the commercialization process. 

The selection and ordering of steps should be unbiased so that no obvious (in retrospect) approach is overlooked. An analysis is normally biased by the chemist s previous experience, and even by the way he draws the target molecule. For example, it is conceivable that the following two representations of patchouli alcohol could lead a chemist to propose entirely different synthetic approaches (from Ref. 5 with permission) ... 

The Retrospective Approach Microbial metabolism studies are conducted after the mammalian routes of metabolism have been elucidated. Such studies can be used to confirm tentative assignments of metabolites in mammals, and support the premise that the same routes of metabolism are observed in both systems. 

A key danger in the retrospective approach is to fall into the trap of conveniently building the safety argument around selective evidence which happens to be at hand. To do so runs the risk of forcing the safety case to articulate an artificially rosy picture of the world. It can be easy to assume that a much-loved system that has been in operation for many years must be intrinsically safe. That is not to say that it is unsafe but one should actively question whether the data which happens to be available can truly and objectively substantiate the safety case s claims. In some circumstances it may be appropriate to undertake the hazard assessment in a virtual vacuum of operational knowledge perhaps involving personnel who are somewhat removed from its day-to-day business. In this way appropriate controls can be developed and more objectively be tested to determine whether they can be traly validated. 

The baseline or reference group may be biased by avoided accidents, as they are not included in accident statistics [12-14, 16, 17]. Although the opinion exists that only accident mitigation can be evaluated by a retrospective approach [12], newer research indicates that the avoidance potential of measures of active safety may be accounted for by statistical means like odds ratios and thus making this constraint less severe [19]. 

The importance of controlling confounders and interaction effects shall be pointed out by an example. Using the retrospective approach, one study evaluated the effects of xenon headlamps on accidents in Germany [20] on basis of the federal accident statistics. As a result, introducing xenon in 100 % of passenger vehicles would lead to a decrease in 6 % of all accidents and 18 % of all fatalities. The study claims that all possible confounders were taken into account and do not bias the results [20], The possible confounders cited, such as exposure time of vehicles, driver behavior... 

Talk to trusted colleagues. Find out what you can about potential service providers. Ask about scope creep driven by the service provider. Then, if you decide to interview a prospective service provider, use the behavioral or retrospective approach, not the hypothetical or prospective method. The behavioral or retrospective method focuses on actual events and actual behavior. In contrast, the hypothetical or prospective method looks forward in an imaginary manner. Here are examples of essentially the same issue posed in the hypothetical and behavioral modes ... 

Retrospective approaches can be applied. In such cases, the analyzed region (that nsed to constmct the depth profile) is defined following data collection. There exist two methodologies that can be used. These are otherwise referred to as Region of Interest (ROI) analysis or Checkerboard analysis. 

With the exception of Bevel SIMS, none of the above techniques remove the loss of depth resolution resulting from the subsurface damage introduced by the sputtering process, i.e. the two go hand in hand. This serves to explain why TRIM simulation tails never completely match SIMS profiles even when all background effects have been accounted for (see Figure 5.19(c) for a pictorial example). Only through bevel approaches or retrospective approaches can SIMS profiles be made to match TRIM simulations. 

Retrospective approaches are more limited as they can only be appUed in ideal cases on atomically smooth spatially homogeneous surfaces if a sufficient amount of information on the system exists. This is realized because such approaches require knowledge of either the instrument s response function (a function that describes the loss of depth resolution apparent under a predefined set of conditions) or the processes describing cascade mixing along with any ion-induced diffusion and/or segregation processes active. Smooth samples are required to ease the computational burden. 

Another factor that has greatly interfered with a systematic prevention of food-borne diseases is the ingrained habit of attempting to supply safe products by relying totally on end-product sampling and examination. It has been demonstrated repeatedly since about 1920 that this system is worthless One of the reasons for this is its lack of sensitivity ". Furthermore, the results of such analyses often become available far too late to recall products and to remedy the situation. One can seldom escape from the impression that the retrospective approach is only followed to provide an alibi. 

---