Defect propagation at the project-level: results and a post-hoc analysis on inspection efficiency

Inspections are increasingly utilized to enhance software quality. While the effectiveness of inspections in uncovering defects is widely accepted, there is a lack of research that takes a more holistic approach by considering defect counts from initial phases of the development process (requirements, design, and coding) and examining defect propagation where defect counts are aggregated to the project-level (i.e., application-level). Using inspection data collected from a large software development firm, this paper investigates the extent of defect propagation at the project-level during early lifecycle phases. I argue that defect propagation can be observed from the relationship between defects in the prior phase and the defects in the subsequent phase. Both Ordinary Least Squares and 3-Stage Least Squares analyses support the hypotheses on defect propagation. Moreover, results show that the inspection efficiency (defects per unit inspection time) decreases as the software product progresses from requirements to design to coding. A post-hoc analysis revealed further insights into inspection efficiency. In each phase, as the inspection time increased, efficiency reached an optimal point and then dropped off. In addition, a project’s inspection efficiency generally tends to remain stable from one phase to another. These insights offer managers means to assess inspections, their efficiency, and make adjustments to the time allotted to inspect project’s artifacts in both the current and the subsequent phase. Implications for managers and future research directions are discussed.