The Impact of Correlated Metrics on Defect Models

Defect models are analytical models that are used to build empirical theories that are related to software quality. Prior studies often derive knowledge from such models using interpretation techniques, such as ANOVA Type-I. Recent work raises concerns that prior studies rarely remove correlated metrics when constructing such models. Such correlated metrics may impact the interpretation of models. Yet, the impact of correlated metrics in such models has not been investigated. In this paper, we set out to investigate the impact of correlated metrics, and the benefits and costs of removing correlated metrics on defect models. Through a case study of 15 publicly-available defect datasets, we find that (1) correlated metrics impact the ranking of the highest ranked metric for all of the 9 studied model interpretation techniques. On the other hand, removing correlated metrics (2) improves the consistency of the highest ranked metric regardless of how a model is specified for all of the studied interpretation techniques (except for ANOVA Type-I); and (3) negligibly impacts the performance and stability of defect models. Thus, researchers must (1) mitigate (e.g., remove) correlated metrics prior to constructing a defect model; and (2) avoid using ANOVA Type-I even if all correlated metrics are removed.