Requirements volatility and defect density

Ideally the requirements for a software system should be completely and unambiguously determined before design, coding and testing rake place. In practice, often there are changes in the requirements, causing software components to be redesigned, deleted or added. This requirements volatility causes the software to have a higher defect density. In this paper we analytically examine the influence of requirement changes taking place during different times by examining the consequences of software additions, removals and modifications. We take into account interface defects which arise due to errors at the interfaces among software sections. We compare the resulting defect density in the presence of requirement volatility, with the defect density that would have resulted had requirements not changed. The results show that if the requirement changes take place close to the release date, there is a greater impact on defect density. In each case we compute the defect equivalence factor representing the overall impact of requirement volatility