Moving on to the session level traffic dimensions which are available under the traffic acquisition report –
These dimensions are designed to work in almost (I say almost because the definition of a session is different in GA4) the same way as the equivalent dimensions in UA. You’ll notice that the conversion column looks completely different because the conversions are attributed based on the last interaction model – as Universal Analytics would have. For example, if a user came to the website using Organic first and then via Paid Search to convert, the conversion will be attributed to Paid Search under this report. You’ll also notice that this report shows the total number of users, which wasn’t available in the user acquisition report.
The third set of traffic dimensions is available under the model comparison report –
This is one report which uses the DDA – as the report suggests. These dimensions are all event-scoped and the DDA model is designed to work at the event level and not at the session and user level, which is the scope of the session and first user level dimensions.
GA4 uses an event-based model meaning the lowest unit of measurement is an event and the DDA model is a complicated algorithm designed to look at data at this lowest level of measurement. This is the primary reason why it’s not available across most reports in GA4 – the DDA is incompatible with dimensions that aren’t event-scoped.
Scope It Out
Understanding scopes can be difficult but it’s not a new concept and was an integral part of Universal Analytics. Not all metrics and dimensions can be combined with each other to produce reports because there might be incompatibility at the scope level. Check out Google’s Help Center to learn more about scopes in GA4.
The only other couple of reports that use the DDA model are –
- Conversions – if you click on a particular conversion type in this report, it opens a screen like this –
- Explorations – if you’re using event-scoped dimensions like the ones shown in the model explorer report screenshot above. A useful feature of explorations is that it greys out dimensions and metrics that aren’t compatible with your selection. This is probably the best place to look at your conversion data attributed using the DDA model. An example below where you can look at your device data with event scoped source / medium attributed using DDA.
All other reports like landing page, device etc. seem to use the last interaction model for attributing conversions as far as we’ve tested.
A useful identifier is that the DDA model’s output is usually in a float format (a number with decimals). This isn’t always the case but if you have a significant number of conversions, you are likely to see conversions with decimals attributed to your dimensions. If you don’t see that in your reports, most likely DDA isn’t being used.