Reliability analysis of “sibling” components

Engineering systems often contain some identical components (parts), the so-called "siblings". In the case of an automobile, these would be engine spark plugs, light bulbs, wheels, etc. These sibling components are typically coded with the same part number. When field (warranty) data are analyzed, a dilemma arises as to how to interpret a recurrent replacement of a sibling component belonging to a given system: as a secondary failure of the component that has already been replaced once, or as the first failure of the component\´s sibling(s)? From the stand point of root-cause analysis, the task is to understand whether recurrent failures are related to 1) a particular sibling, which might be operating in inauspicious conditions relative to other siblings, or 2) to any other siblings on the vehicle. One could attribute Scenario 1) to a system- level (e.g., system interaction) problem, and Scenario 2) to a component-level (supplier quality) problem. This is also critical in selecting an appropriate probabilistic model for predicting the reliability of sibling components. In this paper, we propose a statistical approach that helps to resolve the above formulated dilemma.