To better understand GA4 reporting identities and identity spaces, we strongly encourage you to read about the different methods Google uses in their support article, [GA4] Reporting identity.
To briefly explain, Google uses 4 methods to track users through their journey with your site across devices and platforms. Google refers to these methods as identity spaces:
User-ID - data from signed-in users on your website or app (Google considers this to be the most accurate method)
Google signals - data from users who are signed in to Google
Device ID - anonymous data from a specific device
Modeling - data filled in by Google using similar users’ data when a specific user declines analytics identifiers such as cookies
You will need to determine which identity space(s) you would like to collect for your website and/or app. Not all identity spaces are available to users, and not all identity spaces are enabled by default.
Google determines your reporting identity based on which identity spaces you choose to collect. There are 3 reporting identities in GA4:
Blended - By User-ID, Google signals, device ID, then modeling
Observed - By User-ID, Google signals, then device ID
Device based - Uses only the device ID
Google will report by the first identity space listed in the reporting identity that has data. For example, if you choose to report by blended data, Google will first look for data collected by User-ID. If User-ID data is not found, it will then look for data collected by Google signals, and so on.
Important note about data thresholds
Certain reporting identities are subject to Google's data thresholds. For this reason, Clariti works best with the device-based reporting settings recommended in this article. If you choose blended or observed reporting and have Google signals enabled, there is a possibility that some of your analytics data will be sent to us with thresholds applied.