Behavior Tracking: Why is there a discrepancy in visits between the Referrers and Focus page?

When analyzing visitors using the Behavior Tracking feature of Analytics, you may have encountered that visit numbers between the Referrers and the Focus page don't seem to add up.

To explain why, let's use an example where it looks like there is a discrepancy in visits.

The example below shows that adding all the visits from the different traffic sources amounts to 600 visits. However, when looking at the overall number of visits to the Focus page, they amount to 484.

Siteimprove defines a "visit" as a series of page requests from the same uniquely identified visitor within a time frame of 30 minutes between each page request.

If a user goes directly to example.com, then to example.com/about and then back to example.com in a 30-minute session it will be registered as two different referrers: The first one would be a "direct referrer" and the second would be an "internal referrer".

Both of these referrers will be registered because of the user's journey. However, these two referrers will only be counted as one visit on the Focus page total, since the same visitor was responsible for the two referrers.