Although being important, whether a patch introduces new bugs is very difficult to judge: “introducing new bugs” appears in the top-right corner of Figure 7. This means that although it is highly decisive for rejecting patches,it is in fact very difficult to judge. However, a patch that introduces new bugs decreases the project quality and reliability [25]. Hence, reviewing such a patch is indeed a “high cost, high return” investment: although patch reviewers expend more effort deciding whether the patch introduces new bugs, rejecting it early prevents potentially huge damage on the project’s functionality, long-term maintainability or even reputation.