We’ve all had a similar experience: You log into GA, look at campaign metrics and notice that your extremely targeted campaign has a high bounce rate and low average session duration. How can this be? The more you dig into Google Analytics, the more metric nuances emerge, especially regarding time metrics.In this blog post we will be looking at how Google calculates some of these time metrics, particularly Average Session Duration & Average Time on Page and the differences between these metrics.‍

Definitions

Bounce Rate: The % of users that leave the site from the landing page (single-page sessions). Bounce rate is something to monitor but a higher bounce rate may not always be a negative. Depending on the campaign goals, targeting and/or landing page, a higher bounce rate may be expected.Average Session Duration: The average length of a session. (Formula = Total Session Duration / Sessions)Average Time on Page: The average length of time users spend viewing a page/specific set of pages. (Formula = Time on Page / (Pageviews - Exits)% Exit: The % of pageviews that exited the site from that page. (Formula = number of exits / number of pageviews)‍

Average Session Duration

With standard Google Analytics implementation, Google determines site duration by adding up how long users spend on each individual page. Individual page calculations are based upon navigation and the time it takes the next page to load. This method works pretty well for sessions that visit multiple pages, but what about those users who bounce? Unfortunately, with standard implementation, Google cannot properly measure when a user left a page, so that session is assigned a time of 0:00. This session time of 0:00 is then taken into account during the average session duration calculation.This is why sources with high bounce rates typically have average session durations that are lower.

With this bounce rate over 75%, the average session duration is significantly lower than the site average.‍

Average Time on Page

Looking at the same time frame above with the same source (Direct), we see the Average Time on Page is 1:23. That is over 30 seconds longer than the Average Session duration.

When calculating Average Time on Page, Google Analytics excludes pageviews that it cannot determine a time for (bounces anyone?). Since the pages with times of 0:00 are excluded, this naturally results in a higher average.One important metric to note is % Exit. This is the % of pageviews that left the site from that page. A high % Exit indicates users are leaving the site from this page and will impact our Average Time on Page Accuracy.

Remember that above we said for Average Time on Page, Google does not take into account pages with a time of 0:00? So all of those exited pages will not be used in the average time on page calculation. When a page/group of pages has a higher % Exit, the overall sample size is smaller, making this metric more susceptible to outliers and potentially less accurate overall.‍Hopefully, you now have a better understanding of a few time Metrics in Google Analytics and the nuances and differences between these measurements.