Short summary of a cisco case study (pdf):

“The largest case study ever done on lightweight
code review process; data and lessons”

We believe our results allow us to conclude the following:

• LOC under review should be under 200, not to exceed 400. Anything larger overwhelms reviewers and defects are not uncovered.
• Inspection rates less than 300 LOC/hour result in best defect detection. Rates under 500 are still good; expect to miss significant percentage of defects if faster than that.
• Authors who prepare the review with annotations and explanations have far fewer defects than those that do not. We presume the cause to be that authors are forced to self-review the code.
• Total review time should be less than 60 minutes, not exceed 90. Defect detection rates plummet after that time.
• Expect defect rates around 15 per hour. Can be higher only with less than 175 LOC under review.
• Left to their own devices, reviewers’ inspection rate will vary widely, even with similar authors, reviewers, files, and size of the review.