Testing the theory of relative defect proneness for closed-source software

Recent studies on open-source software (OSS) products report that smaller modules are proportionally more defect prone compared to larger ones. This phenomenon, referred to as the Theory of Relative Defect Proneness (RDP), challenges the traditional QA approaches that give a higher priority to larger modules, and it attracts growing interest from closed-source software (CSS) practitioners. In this paper, we report the findings of a study where we tested the theory of RDP using ten CSS products. The results clearly confirm the theory of RDP. We also demonstrate the useful practical implications of this theory in terms of defect-detection effectiveness. Therefore, this study does not only make research contributions by rigorously testing a scientific theory for a different category of software products, but also provides useful insights and evidence to practitioners for revising their existing QA practices.