Comparing high-change modules and modules with the highest measurement values in two large-scale open-source products

Identifying change-prone modules can enable software developers to take focused preventive actions that can reduce maintenance costs and improve quality. Some researchers observed a correlation between change proneness and structural measures, such as size, coupling, cohesion, and inheritance measures. However, the modules with the highest measurement values were not found to be the most troublesome modules by some of our colleagues in industry, which was confirmed by our previous study of six large-scale industrial products. To obtain additional evidence, we identified and compared high-change modules and modules with the highest measurement values in two large-scale open-source products, Mozilla and OpenOffice, and we characterized the relationship between them. Contrary to common intuition, we found through formal hypothesis testing that the top modules in change-count rankings and the modules with the highest measurement values were different. In addition, we observed that high-change modules had fairly high places in measurement rankings, but not the highest places. The accumulated findings from these two open-source products, together with our previous similar findings for six closed-source products, should provide practitioners with additional guidance in identifying the change-prone modules.