Why Time On Page Is Inaccurate

by admin on 02/12/08 at 10:20 am

When considering the time on page that Google Analytics reports, you have to remember that this can be a very inaccurate metric. Let’s first understand how Analytics calculates the time that a user spends on a page.

How Google Analytics Calculates Time On Page

Each time a page on your site loads, Analytics records the timestamp. If a visitor navigates from page A to page B, Analytics records two timestamps: one identifying when page A was loaded and the other identifying when page B was loaded. It’s then easy to calculate the time spent on page A:

time spent on page A = timestamp 2 – timestamp 1

However, now imagine that the visitor navigates to a new page not on your site or closes down their browser altogether. There has been no further page load to trigger Analytics to record a timestamp, so there is no way for us to calculate time spent on page B. Thus, if page B is the exit page, we cannot know how long the visitor stayed there.

This relationship between the accuracy of the time on page metric and the exit rate for that page can be illustrated thus:

Time on Page is more accurate when the page has a lower Exit Rate

Extending this further, if the exit rate for a page is 30%, the time spent on that page applies to only 70% of its visitors. For the other 30% of visitors who exited the site from that page, Analytics can’t determine how long they spent there.

How Google Analytics Calculates Time On Site

Analytics does a similar thing when calculating the time a visitor spends on your site. Bear in mind that every visitor exits the site at some point. Time on site is calculated by subtracting the timstamp recorded when the visitor first hits your site from the timestamp recorded when they land on the last page. Of course, this time excludes the time spent on the final page as this is impossible to determine (see how time on page is calculated above). Therefore, single page visits, or bounces, contribute nothing to the time on site value.

This leads us to conclude that the more bounces a site has, the less accurate the time on site value is.

Google Analytics