Why do my google analytics unique-user counts not match the data?

2
votes

We've implemented Google Analytics in our site, tracking user-id in both the tracker's userId property, and a custom dimension. The problem is, while the custom dimension shows the number of distinct values we expect, the user-id is being tracked inconsistently.

For example: in a given period where we expect four unique visitors to be reported, we get that from our custom dimension, but the user-id shows only three. Drilling down gives us this report:

4 different user-ids; totalled to three

(this example uses data from the 14th-16th, and was run on the 17th)

There are clearly four rows - as expected - but the total is showing as three. What's going on here? Am I misunderstanding the way GA tracks users?

Extra info:

  • Our site is a subscription site so users have to login at the beginning of their session and we use the unique identifiers provided by our authentication system for UserID.

  • We checked our unfiltered UserID view and the user count there is correct, so we are thinking this might be a problem with one of the filters applied on the main view. One of the users logged in at work and then from home the next day during the date range in question, so could the internal traffic filter be interfering with the user count?

  • The site's traffic is currently very low (as the number of users implies,) and the date range is very small so I wouldn't expect any sampling to be happening.

1
webgoogle-analytics
Isn't possible, that one ClientID have more UserIDs? What is the time range? How long from data collection you run this report? - Jakub Kriz
I've added the date clarification to the question; in terms of client-id, my understanding is that ClientID is irrelevant here because we are using User ID, and passing the exact same value in both the custom dimension and the tracker. In the views where the User ID feature isn’t turned on and GA relies on ClientID to recognize users, we are getting expected results (a single user ID in the custom dimension being counted as two users for instance, when they logged in with their desktop and then their phone, or from work and then from home). - Will Goring
It took me longer time to think about it, but how do you create UserID? Is it based on users email address? Is possible that during one session can user have two UserIDs and same ClientID? If it works with ClientID and non UserID feature, it have to be somewhere in between. Either some sampling can get into this (if you are not a premium user). - Jakub Kriz
I've added some more relevant info to the question. My understanding of the User ID feature is that sessions are linked to a specific ID, so if you were to logout and log back in using a different set of details, and therefore be given a different User ID, then this should be considered a new session. In which case, if your ClientID is the same, then the session count should be different between the main view which uses ClientID and the User ID view. The session count is the same on both our views, only the user count differs, so this can’t be it. - Will Goring

1 Answers

0
votes

The ga:users metric counts unique users (or, more precisely, unique browser cookies), so the total value for several days is not the sum of values for each single day. This is because a user that visits your site on multiple days is only counted once when computing the total for a day range.

For example, you have users A, B, and C.

On 2015-01-01, your site is visited by A and B.

On 2015-01-02, your site is visited by A and C.

This means two unique users on 2015-01-01 (A and B), two unique users on 2015-01-02 (A and C), and three unique users for the period 2015-01-01 until 2015-01-02 (A, B, and C).

Also, there can be small discrepancies because of the way GA optimizes the calculation of ga:users. More details can be found in the Analytics Help.