How Sawmill calculates Sessions
How does Sawmill compute session information?
Question: How does Sawmill compute session information, like total sessions, repeat visitors, paths through the site, entry pages, exit pages, time spent per page, etc.?
Answer: Sawmill computes session information (via the Sessions snapon) by tracking the page, date/time, and visitor id (which is usually the hostname (client IP)) for each page view. This session analysis occurs as part of the database build, when the Database Filter of the Sessions snapon is run.
Sawmill groups the page views into initial sessions based on the visitor id-- it starts by assuming that each visitor contributed one session. It sorts the hits by date so it has a click-by-click record of the movement of each visitor.
Then it splits the sessions, using the session timeout interval (this is set to 30 minutes by default but your Sawmill Administrator can change this). Since most web sites are accessible without logging in, there is no way for Sawmill to know the real time that a user leaves the site; it can only guess by assuming that if they didn't click anything on the site for 30 minutes, they must have finished and left. By splitting the sessions up in this way we are counting more accurately the number of sessions a given visitor has had on the web site. It is not a perfect science, but over time, as long as the method of measuring remains the same, a trend can be found. This splitting process increases the number of sessions that Sawmill counts, resulting in possibly more than one session per visitor.