The golden rule for creating accurate GA4 reports

If you don't know/follow the golden rule for creating GA4 reports, you will make mistakes like the one shown in the screenshot below:

So what’s the mistake here?

The 'First User Default Channel Group' dimension has a 'user' scope. The 'source/medium' dimension has the 'event' scope.

Combining these two dimensions with different scopes creates a mismatch in the detail level they represent, resulting in inaccurate data (like 100% user key event rate, 100% session key event rate, etc).

Pair the "First User Default Channel Group" with the 'First user source/medium' dimension.

The other issue with this report is that you can't query the "First User Default Channel Group" dimension or the "First user source/medium" dimension with the "sessions" metric.

This is because these dimensions and metrics belong to different scopes.

First User Default Channel Group and First User Source/Medium are user-scoped dimensions. Sessions is a session-scoped metric.

User-scoped dimensions aggregate data across all sessions for a user, while session-scoped metrics focus on individual sessions.

User-scoped dimensions provide a big-picture view of a user, while session-scoped metrics zoom in on individual sessions.

That's why mixing user-scoped dimensions with session-scoped metrics can lead to inaccurate data in your reports.

GA4 supports three different scopes for dimensions and metrics: user scope, session and event scope.

Each scope represents a different level of data aggregation and context.

These scopes should never be mixed in GA4 reports. Otherwise, it results in a 'scope mismatch' error.

Remember my golden rule for accurate GA4 reporting:

"In GA4, reports should only be created with all the dimensions and metrics belonging to the same scope."