Safety intervening variables

But simply replicating the results does not validate them. The issue of validity is most often involved when we assume intervening variables and rely on surrogate measures of safety (rather than crash involvement). Thus, we should always question the validity of findings that are based on research in driving simulators and in studies relying on drivers self-reports or responses to questionnaires. In neither instance do we measure actual driving behavior, and in neither case do we know how to consider the accidents relative to real ones. 

One portal type was considered in the examples. This frame had 6 stories and 3 bays. The reliability levels corresponding to three performance requirements (operational, life safety and collapse) were obtained for seismic conditions corresponding to the city of Mendoza, Argentina. Characteristics of all the intervening random variables are shown in Table 2 and the mean value of those marked with the symbol are the design parameters considered in the optimization. 

Other words, safety cannot be managed by imposing constraints on how work is done. The solution is instead to identify the situations where the variability of everyday performance may combine to create unwanted effects and continuously monitor how the system functions in order to intervene and dampen performance variability when it threatens to get out of control. At the same time, we should also keep an eye on situations where variability may have useful effects, and learn how to manage and reinforce that. 

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