reliability is extremely useful to help guide early design changes, and any such early assessment must be based on a combination of information from a variety of sources given the scarcity of direct assessment early in system development. Therefore, combining information, some of it possibly subjective, is likely to prove beneficial in some situations.

It is becoming increasingly common—though by no means widespread as yet—for reliability assessment for industrial systems late in development to make effective use of information on the reliability of related systems (e.g., systems with identical or similar components) and information for the same system from laboratory testing. Even earlier in system development, some industries have demonstrated the utility of information on related systems and expert judgment to help make initial assessments of system reliability that are useful for developmental test planning and for tracking of reliability growth.

In the field of statistics, combining information models are currently being developed primarily from a Bayesian perspective. Much progress is occurring in this area as a result of the development of simulation methods that have greatly facilitated the calculation of Bayesian estimates. This rapid progress increases expectations that more and more types of applications will be addressed using these new methods.

Certainly such methods cannot be used without some scrutiny, and the benefits of use of these models for defense systems will almost undoubtedly vary with the specific application. The linkage between failure modes and failure frequencies across systems and across environments of testing or field use must be well understood before these models are applied. Aggressive efforts are needed to validate the assumptions made. The expectation is that over time, estimates for some measures for some types of systems will be found to benefit greatly from use of these models, whereas for other systems, these models will be much less useful. Chapter 3 provides a description of some specific methods that were suggested for use at the workshop.



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