Evolution and errors: an empirical example

An empirical study is presented that explores how dangerous errors can be introduced into software by the simplest of maintenance tasks. Six different maintenance problems were given to eight intermediate level programmers. Each maintenance problem was coded using the C++ language and were selected from a domain that was deemed to be familiar to all subjects. An alarming level of error was discovered. Analysis of the maintained software showed that one third of all the resulting programs contained an error of some form. Reasons why the error rates were so high are considered and two broad approaches to the reduction of maintenance error are described.