Session Unification in Google Analytics

Timothy Yuen - Wednesday, March, 09, 2016

Those of us who spend their working lives up to their elbows in Google Analytics – like I do – take a lot of its great functions and quirky complications for granted.

So I’ve decided that now is a good time to start sharing some of my knowledge to help you get the most out of this incredibly powerful tool. There will be many interesting conversations to come!

To start with, I have recently been looking at the User ID setting for session unification and I thought I’d share a recent discovery with you. It will help you understand some of those mysterious gaps in your User ID view.

While doing some testing, I’ve discovered a User ID issue, related to session unification, that many of you may not even notice. Until now, I had always thought that all hits before the User ID is set would be unified as coming from the same User. It turns out that this is incorrect.

Session unification only happens for all hits before the first hit containing the User ID. Any hits without the User ID, after the initial hit, are not counted.

What are the implications of this you ask?

Well, imagine you are tracking the User ID when a user logs onto your site. That user logs out, or times out, browses a few pages and then they log back in – still within a session. Their User ID will not be logged in the few pages they browsed after logging out. And any subsequent pages they view or events without the User ID will no longer be tracked or unified into the session.

I had a sift through the Google Analytics documentation, looking for some clarity, and all I could find was this cryptic sentence:

Now that we know this, what should we do?

As per the Google Analytics statement, ALL hits should contain the User ID once it is known. But if it is not known or tracked, you may face some sticky questions about why certain pages or data are missing in the User ID view.

You’re probably wondering, “how on earth do I go about explaining that missing (in between) data to senior management?” And it’s all about the user choosing to maintain their privacy.

If the user has chosen to ‘log out’, then their subsequent pages/events aren’t tracked. By logging out they have opted out from being tracked.

I believe that this is the basis of the Google Analytics logic for not automatically tying together all of a user’s sessions, once their user ID is identified. The missing data is adhering to, and protecting, the privacy of the user.


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