Average Session Duration in Google Analytics
Th average session duration in Google Analytics is an often used metric to understand the engagement of your website audience. Per Google Analytics, it is calculated as:
Average Session Duration = total duration of all sessions (in seconds) / number of sessions
Engagement Hits on Last Page
As you enter the landing page of SeoHighLighter, for example, Google Analytics tracks the time from the first hit on the landing page to the last hit on the last page you visit. For example, you start on the landing page, check out the FAQ section, and then find yourself on this blog post. You read it and navigate back to Google.com. Because you left SeoHighLighter, Google Analytics can track the time at which you left this site.
You’re Browsing and Leave for Lunch
However, what if you are browsing SeoHighLighter.com, for example, landed on the home page and are now reading this post and then leave for lunch. Google analytics has no clue how long you have spent reading this blog post.
Basically, when you don’t click anything else on my site or navigate away from my site, it stops the session duration at the time you first entered this blog post (assuming it was the last page your are reading on my site and then left for lunch).
Also, if you have high bounce rates, your session duration will drop because, again, GA doesn’t know how long spent reading this post if there is no last engagement to record another point in time.