A system-level reliability-growth model

Using a subsystem growth model developed by the authors together with the concepts associated with the composition of moments, the problem of system-level growth analysis is considered. It is shown, using the moments of the subsystem failure rate distributions as they change during test, how the moments of the distribution of the system level failure rate can be estimated. Then, using these moments, point estimates and approximate confidence intervals for system reliability growth can be calculated. A simple hypothetical example is presented to illustrate some of the nuances of the analysis methodology. This is followed by two actual situations where the growth model is used to analyze development progress at the system level. These two examples are based on data collected during the development of two systems; the first is a simple system of three components, while the second system is composed of eleven subsystems in a more complex structure