From the "Topic list" screen (see Section 3.2), clicking on "Metrics Report" will take you to this page. An example screenshot can be seen in Figure 3-14.
As it can be seen, this page presents aggregated views for user metrics over the past 16 weeks, and topic metrics over last year, aggregated by month. For a real software team, this page will provide a wealth of detail as to how effective code reviews are. There is a link at the bottom of the page for retrieving this information as a CSV file, which can then be imported into other tools.