This is a question that I not only am asked every now and then, but it also is something I think to myself from time to time as I just cannot seem to remember or make sense of the explanation behind it without going through the whole thing again.
Intro / Google Analytics
You no doubt know that Google Analytics is the most widely used webpage analytics program and is used to track all sorts of interactions on and with websites. This include stuff like number of visitors, number of sessions, page views, and more. You can sort what you are looking at by hour, day, week, month, or custom range.
I basically use Google Analytics on almost all the websites I work on, unless clients specifically ask me not to. Google Analytics is a great program, and Google keeps updating it constantly to try and improve it. There is one area, one big thing, that I am not crazy about with Analytics. It really isn’t something Google can fix and other programs have this issue to.
The issue is that Google Analytics (and other tracking software) can only track based on hits. So when you go to a page, that is a hit. When you go to another page, that is a hit. In that example, Google knows when you went to the first page and when you went to the second page. However, if you then leave the website, Google has no idea how long you spent on the last page (unless there was some sort of hit or engagment hit on the last page that they could track).
Engagment hits are defined as:
An engagement hit is any hit that is not marked as “non interaction” and is not filled only with custom variable information. This means that the hit has at least page information, ecommerce transaction information, ecommerce item information, event information or social tracking information
So the session duration is calculated as last hit time – first hit time = session duration (so like 12:10 – 12:00 = 00:10 or 10 minutes). They then get an average by adding up all the session durations and dividing by number of sessions. What this means is that if a session has two page views and a session duration of two minutes, you really only know that they spent two minutes on the first page and don’t know what happened on the second page. Maybe they stayed there for another two minutes. Maybe they left immediately.
Time on Page
Lets then look at page duration. It works the same way as session duration. Hits are tracked and it is the time difference between hits for each page that is the page duration. So if you land on page one, then go to the next page two minutes later, the time on page one is two minutes. They then calculate average time on page by totaling all the time on a page and dividing by the number of views of that page.
Things get really tricky when people only go to one page (or have one engagement hit i.e. a bounce). Unless there are engagement hits, Google doesn’t know how long people spent on that page, and so, they don’t give a time on page. They then do count that visitor as a 0:00 session duration. This in turn then messes up the stats in your analytics account and can make it look like people aren’t as engaged with your site as they really are.
What this all means
So why bother talking about this at all? Well, basically I am saying that Google Analytics, and other tracking programs, aren’t all that accurate without doing extra work to make them so, and even then it might not be tracking right.
If you want your analytics to be more accurate, you can ad engagement hits to your site, which then can be used for more accurate tracking. Otherwise, those bounces or one page visits are not getting tracked.
The way Google does things also results in messed up analytics where the average session duration can be really low and the average time on page can be high. I have sites that regularly have a bounce rate of 70% with an average session duration of 30 seconds, but then the average time on pages are all like three to five minutes. What is happening is all those bounces, which are counted as zero, are dragging down the average session duration, but they aren’t counted in the page views.
This also means that Analytics doesn’t really work for when you are getting traffic from places like StumbleUpon, where users read your page, then click a button to go to another recommended website. Unless they trigger an engagement hit, all that traffic is counted as a session of 00:00. while the page views rack up.
In the end, this doesn’t really mean a whole lot for your site. You still want to get traffic, even if they do bounce. Adding engagment hits could be worth it if you have time or you can set up something that requires no work, like Jetpack related posts at the end of posts to get users to click on another post. Google does consider user actions in the SERPs, but as far as I can tell time on page and session duration are not particularly used for that. They instead rely on clicks.