Most business decision have considerable uncertainty which implies at least two outcomes if you choose a course of action. Making decisions in the face of uncertainty requires the costs for taking action and the probability along with the cost for not taking action and the probability of the occurrence. In most cases the probabilities are not well known (maybe to one significant digit) and the costs are not well know (maybe to $10000). The quantitative assessment is called risk assessment. The issue is to take these not well identified issues and devise a strategy which can minimize exposure to risk for the business. The graphical representation of the methodology is called decision trees to reach the expected values for decision to take/not-take action.
Why: Data is the information that, when used in an informed manner, helps prevent repetition of bad history and allows an enlightened approach to rationally solving a reliability issue using facts and figures. Intelligent use of data for reliability issues provided the objective evidence needed for helping to solve the root cause of failures.
When: Databases of reliability information of past experience is very helpful for predicting future failure events. The data is helpful if failure rates, or the reciprocal of failures rates is described in mean times to failure which reduces the information to an average failure rate or average time to failure. The reliability data is particularly valuable if retained for components as a Weibull data base with shape factor beta and scale factor eta.
Where: The data is useful for understanding failure modes, and for predicting future failures for a population of equipment during the design stage and for predicting future failures with subsequent increases in the aging of equipment. The role of the reliability engineer is to acquire the failure data and convert the data into useful information for both current and future use.
These definitions are written by H. Paul Barringer and are also posted on his web site at www.barringer1.com
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