I was thinking the same thing. I was expecting them to analyze the diffs and keep a cache of code blocks that are changing in each bugfix. Keeping track of bugs at the class/function/method level would seem to be more powerful.
Existing research points to "number of bug-fixing commits" as being enough to predict.
I would assume that's due to the fact that bugs are not always constrained to a single function, but usually to closely related code. Which often means all that related code is in the same file.
Indeed. Also, typically code "ownership" is at the file level -- and that's likely to correlate strongly with defects in situations where a peron who hasn't been well trained (or is just a bad programmer) is writing or maintaining the code.
