Most teams treat code review as a defect filter. The research says that is the wrong scoreboard.

Bacchelli & Bird (ICSE 2013) studied modern code review at Microsoft. They surveyed 873 engineers and analyzed reviewer comments across multiple teams. The headline finding is uncomfortable: "finding defects" is the most-stated motivation for doing code review — but defects are not what dominates the actual review output.

Most comments fall into:

Code improvement suggestions — refactor this, simpler approach, name it better.

Knowledge transfer — explaining why the existing code looks the way it does, surfacing context only one teammate had.

Awareness and team alignment — teaching the reviewer about a part of the system, socializing a design choice across the org.

Defects — present, but a minority of comments.

The implication for how we run reviews is real.

1. Stop measuring reviewers by defects found. That metric optimizes for the wrong thing.…