Google Analytics Changes Session Definitions

If you weren’t paying close attention yesterday you may have missed a small announcement from Google about an update to sessions in Google Analytics. It’s a small update that will affect less than 1% of total users, but if you’re in that 1% of users (or have your analytics set up wrong) you may see some crazy effects.

Here’s what Changed:
Sessions used to end at the end of the day, after 30 minutes, or when the user closed the browser. Now, a session will no longer end when a user closes their browser and can alsoend when a user’s utm parameter changes. That last one’s the important one.

What?
Basically, if I come in to your site from a paid search ad, that’s a session. If let’s say 20 minutes later I click on a link in a tweet with a ?utm_source tag. Previously that would be part of my same open session. Now however Google Analytics will end that old session and start a new one.

Why?
This solution provides better attribution for campaigns. Basically, it’s GA switching to a last-click attribution model. There’s plenty of arguments about whether last click, first click, or weighted attribution are best but I’ll leave that for another post.

Let’s talk about potential issues
According to Google, 99% of users won’t see a problem. If you’re seeing your visits significantly rise for no reason though, you might be in that other 1%. You’re bound to see some small increase in visits due to the browser closing change, but some sites will huge changes. Here’s how that can happen:

Suppose you set up your Google Analytics lazily or just plain wrong. For some reason (and there’s a lot of websites who I won’t pick on that are doing this) you put ?utm_source on your internal site links. Perhaps it’s a promo box on your homepage that links to one of your other pages and you want to track it as a campaign – an easy mistake for a novice to make.

Under the old system, there was no problem here. Under the new system though you’ve got an issue. Now, anybody who clicks on that promo box is essentially ending their current session and starting a new one! That could throw off your total visits / sessions and any calculations that use them.

The solution here is to make sure you’re not using any ?utm_ parameters on your internal site links. That’s not what they were made for. There’s a lot of great ways to track that type of thing in Google Analytics (all beyond the scope of this blog post and better answered by the Google Analytics Help files.)

In light of the recent change though, now is a great time to re-check your analytics implementation and make sure everything’s working as it should.

August 17th, 2011