Beware that by introducing measures, people will optimize for the measure, not for the intended goal.
- If you measure the number of lines of code removed per defect, people will remove lines.
- If you penalize the number of lines added, people will not add lines of code.
- If you penalize the average time to fix, people will quickly/immediately close bugs, either as "not a bug" or as "fixed", regardless of whether that's true.
The underlying question of whether what people do actually makes sense in the context given (removing lines of code likely reduces the code complexity and hence is "good") is not easily answered by these metrics, and such metrics will pull people into the direction of gaming the metrics.