Last week, the Google Analytics Team announced it was modifying how they track sessions. This change will not affect your historical data, rather, it will affect only data going forward. Based on its research, the Google Analytics Team expects that most users will see less than a 1% change in the number of visits.
So what is changing? In the past, Google Analytics ended a session when one of the following occured:
1. More than 30 minutes elapsed between pageviews for a visitor
2. End of the day
3. Visitor closes their browser
With the update, number three in the above list is modified to end a session when any traffic source changes. For example, if a visitor reaches your website via an AdWords ad and then comes back to your site via a different campaign or traffic source (within 30 minutes), the initial session will be ended. In turn, this will establish a new visitor session.