I'm trying to figure what the difference is between metrics "Average Time Spent on Site" and "Time Spent per Visitor".
Here is the documentation for "Average Time Spent on Site". Definition: "Average Time Spent on Site is the amount of time (in minutes) users have spent on your site across all visits."
There is no specific page for "Time Spent Per Visitor" (why not?), but I did find it referenced in the "Time Spent" page. Definition: "Represents the time spent for a visitor during the selected date range.
For example, if a visitor made 5 visits to the site during the selected date range, and spent a total of 40 minutes on the site, Time Spent metrics (per visitor and visits) are calculated as follows:
Time Spent per Visit (40 mins, 5 visits) = 8 minutes
Time Spent per Visitor (40 mins, 1 visitor) = 40 minutes"
Now if I just look at the definitions, these are the same metrics! You're getting the time spent per user across all their visits. Why are there these two metrics?
In practice, however, these two metrics do not yield the same values. It appears that Average Time Spent on Site is always lower than Time Spent per Visitor. I can recreate the Time Spent per Visitor well enough using Total Seconds Spent and Unique Visitors using a single page visit segment. This is not 100% accurate since we can get the time for a single page visit if there's an event that takes place on that single page visit (other than the page load), but for some reason in AA you cannot segment out Visits that are Bounces (why?! but that's a separate story). What I cannot reproduce is Average Time Spent on Site. The documentation actually does not explain how this is calculated.
So, how are these two metrics different? How specifically is Average Time Spent on Site calculated?