ELBlocker: Predicting blocking bugs with ensemble imbalance learning

ContextBlocking bugs are bugs that prevent other bugs from being fixed. Previous studies show that blocking bugs take approximately two to three times longer to be fixed compared to non-blocking bugs.ObjectiveThus, automatically predicting blocking bugs early on so that developers are aware of them, can help reduce the impact of or avoid blocking bugs. However, a major challenge when predicting blocking bugs is that only a small proportion of bugs are blocking bugs, i.e., there is an unequal distribution between blocking and non-blocking bugs. For example, in Eclipse and OpenOffice, only 2.8% and 3.0% bugs are blocking bugs, respectively. We refer to this as the class imbalance phenomenon.MethodIn this paper, we propose ELBlocker to identify blocking bugs given a training data. ELBlocker first randomly divides the training data into multiple disjoint sets, and for each disjoint set, it builds a classifier. Next, it combines these multiple classifiers, and automatically determines an appropriate imbalance decision boundary to differentiate blocking bugs from non-blocking bugs. With the imbalance decision boundary, a bug report will be classified to be a blocking bug when its likelihood score is larger than the decision boundary, even if its likelihood score is low.ResultsTo examine the benefits of ELBlocker, we perform experiments on 6 large open source projects – namely Freedesktop, Chromium, Mozilla, Netbeans, OpenOffice, and Eclipse containing a total of 402,962 bugs. We find that ELBlocker achieves F1 and EffectivenessRatio@20% scores of up to 0.482 and 0.831, respectively. On average across the 6 projects, ELBlocker improves the F1 and EffectivenessRatio@20% scores over the state-of-the-art method proposed by Garcia and Shihab by 14.69% and 8.99%, respectively. Statistical tests show that the improvements are significant and the effect sizes are large.ConclusionELBlocker can help deal with the class imbalance phenomenon and improve the prediction of blocking bugs. ELBlocker achieves a substantial and statistically significant improvement over the state-of-the-art methods, i.e., Garcia and Shihab’s method, SMOTE, OSS, and Bagging.