Research Report: Modeling the Incidence of Postrelease Errors in Software

Error search and correction are major contributors to software development cost, yet typically uncover only a small fraction of software errors. Postrelease errors, i.e., those that are only observed after a system is released, threaten a variety of potential failures and consequences, each with low individual probability of occurrence. The combined effect of postrelease errors can and often does result in a significant rate of occurrence of these potential failures, with unpredictable consequences and severity. One particular source of postrelease errors that has received extensive publicity is the year 2000, or Y2K, error. The modeling in this research report suggests that testing probably needs to be conducted over more than half of the useful life of a system in order to discover even one-third of the total errors in the system. It suggests that short product lifecycles, lifetime testing, and effective feedback loops for error reporting are necessary to assure reliable software.