In life data analysis and accelerated life testing data analysis, the objective is to obtain a life distribution that describes the times-to-failure of an item.

For any life data analysis, the analyst chooses a point at which no more detailed information about the object of analysis is known or needs to be considered. At that point, the analyst treats the object of analysis as a "black box." The selection of this level (e.g., component, subassembly, assembly or system) determines the detail of the subsequent analysis. 

In system reliability analysis, a "system" model is constructed from these component models. This enables the construction of a model (life distribution) that represents the times-to-failure of the entire system based on the life distributions of the subsystems, assemblies and/or components ("black boxes") from which it is composed.