A conservative theory for long term reliability growth prediction

Abstract

The paper describes a different approach to software reliability growth modelling which should enable conservative long term predictions to be made. Using relatively standard assumptions it is shown that the expected value of the failure rate after a usage time t is bounded by: /spl lambda/~/sub t//spl les/(N/(et)) where N is the initial number of faults and e is the exponential constant. This is conservative since it places a worst case bound on the reliability rather than making a best estimate. We also show that the predictions might be relatively insensitive to assumption violations over the longer term. The theory offers the potential for making long term software reliability growth predictions based solely on prior estimates of the number of residual faults. The predicted bound appears to agree with a wide range of industrial and experimental reliability data. It is shown that less pessimistic results can be obtained if additional assumptions are made about the failure rate distribution of faults.