Understanding the discrepancies between Universal Analytics and GA4

Ken Bandong
February 16, 2023

Why am I seeing data discrepancies between Google Universal Analytics and Google Analytics 4?

When you have successfully completed your GA4 migration, one question that comes to mind is how is it different from Universal Analytics and why do I see different data? 

As we have previously discussed in this blog on the difference between GA4 vs Universal Analytics, Universal Analytics is completely different from GA4. The main difference is that GA4 uses a different data model compared to Universal Analytics. 

To give a high level recap, Universal Analytics measures a web-based session data model whereas GA4 operates on cross-device and platforms using an event-based data model for measurement.

You may want to constantly compare your UA data to GA4 especially when you have just recently migrated and have set up parallel tracking. 

In this article, we are going to discuss what is the reason behind the discrepancy and our recommendation on how to address the differences.

How to Address the Differences Between GA4 and UA Metrics

Apart from the data model difference, there are a lot of factors that can cause the discrepancy such as tagging and configuration settings. 

One should always check whether this is the same for UA and GA4:

  1. Both tags are installed on the website correctly
  1. Event tags are firing when triggered
  2. The same timezone is used
  1. Comparing an unfiltered data view or stream
  2. Dimension and metric definitions

That being said, when you are looking at your UA data it is highly likely that you will see discrepancies with GA4. Not only that, dimensions and metrics may look and sound the same but it is important that we understand how GA4 defines it. You may check this article on comparing the differences between UA and GA4 metrics here.

Example of differences:

Here’s a screenshot of one of our accounts using GA4, showing Users and Sessions for the same period:

For Google Universal Analytics

The difference in data could be attributed to the difference in which metric is primarily used for user in each platform. Universal Analytics uses Total Users whereas GA4 uses Active users. It is also important to note configuration settings can contribute to this discrepancy.

I don’t really recommend comparing your data between UA and GA4 but it can be useful to some extent. We can use this to compare whether GA4 tracking was successful and correct but it is important to keep in mind that when we make this comparison, UA and GA4 should have tagging and configuration settings as explained earlier.

It is important to understand the difference between the two platforms because you not only understand and familiarize yourself with GA4 but give the leverage to easily discuss with your client why such discrepancies appear to better to optimize campaign and marketing efforts.

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