Relating Alternate Modifications to Defect Density in Software Development

A software developer tends to spend more effort to understand source code written by other developers than code written by herself. Existing research studying the impact of changes made by multiple developers on bug proneness did not consider quantitatively the influence of the order of the changes made by different developers. We found that a significant proportion of source files in many open source software systems had been modified alternately by different developers. We developed a metric, namely alternate modification index (AMI), to indicate the extent to which a source file is modified alternately by multiple developers. Our preliminary case study results show that AMI of source files has a strong positive correlation with their defect density.