Code reviews are inadequate at finding bugs.¹¹¹ Jacek Czerwonka and Michaela Greiler, “Code Reviews Do Not Find Bugs. How the Current Code Review Best Practice Slows Us Down” (paper, May 2015). 

If code reviews were good at finding bugs, then codebases that require two or more code reviews would be the better codebases. In practice, the opposite is more likely to be true.

Better approaches to finding defects include manual QA, and automated testing (preferably good end-to-end test coverage).

To do: read Chris’ response to the Microsoft research article. The original article has odd phrasing and is of dubious quality. My own experience in code reviews not finding defects is purely practical, and not based on that article.