Understanding the Occurrence of Multiple User Pseudo IDs with GA4 Session IDs

[Brooke]

Certainly, I’d be happy to simplify.

The situation you’re experiencing is normal and has to do with how sessions are identified in Google Analytics 4. Essentially, a unique session in GA4 isn’t determined solely by the session ID, but rather by a combination of both the session ID, or ga_session_id, and the user_pseudo_id.

So, you might run into a situation where it appears two different user_pseudo_ids are associated with the same ga_session_id. But remember, it’s the combo of these two that identifies a unique session, not just the session ID alone. Basically, GA4 is designed to work this way!

If you want more info, you can check out an article I put together explaining how to identify and calculate sessions on the official Google Analytics Developers page. I sure hope this clears things up!

[Michael]

Sure, let me break this down as simply as I can. Google Analytics 4 (GA4) assigns each browsing session a unique ‘session ID’ and each user/visitor a ‘pseudo ID’. This helps it track how users are interacting with your website. Normally, each session ID should be associated with only one user (or pseudo ID), but you have discovered that some session IDs are tied to two different pseudo IDs. This is unusual and seems to suggest that two different users are somehow sharing the same browsing session.

Now, you tried testing this by deleting cookies partway through a session, but that wasn’t the cause. This is because GA4 keeps using the same pseudo_ID for a user even if cookies are deleted midway.

One plausible explanation is that GA4 sometimes assigns the same session ID to multiple browsing sessions that start at the exact same time. That’s why it is important to consider both the session and pseudo IDs when doing your analysis. The combination of the two helps you more accurately track unique browsing sessions.