What is the Session Scope?

Session-scope means the value of the dimension is calculated and sent once for each session. 

This means that each time a user starts a new session, the session-scoped dimensions are recalculated based on the context of that particular session.

What is the GA4 Session-scoped dimension?

GA4 Session-scoped dimensions provide insights into where both new and returning users are coming from when they start new sessions, such as the source and medium through which the user arrived during that session.

Session-scoped dimensions in GA4 primarily capture information specific to the current session, not necessarily across all sessions or user journeys. They provide context about the user’s interaction within that specific visit.

Example:

Dimension: Session source/medium

Value: “google / organic” (for the first session), “direct / (none)” (for the second session)

If a user first visits your website through an organic search on Google, the “Session source/medium” dimension will be set to “google / organic” for that session. 

If the same user returns to your website directly (by typing the URL into the browser) in a subsequent session, the “Session source/medium” dimension will be updated to “direct / (none)” for that session.

However, if the user first visits your website through an organic search on Google and then returns to your website directly midway through the session, the “Session source/medium” dimension will remain  “google / organic” 

Note: GA4 does not start a new session if the traffic source, medium, or campaign changes mid-session. 

Importance of Session-scoped dimensions

Session-scoped dimensions help analyse how users interact with your website or app during specific sessions, which can be useful for:

1. Traffic Analysis: Understanding where users are coming from during each session.
2. Behavior Analysis: Analyzing user behaviour within specific sessions to identify patterns or issues.
3. Conversion Tracking: Tracking conversions and key events within individual sessions.

GA4 Built-in session-scoped dimensions

GA4 has only one category of session-scoped dimensions called the GA4 Built-in session-scoped dimensions. 

These are ready-to-use dimensions available in the GA4 reporting interface or data API.

The following table provides a brief description of the various GA4 Built-in session-scoped dimensions:

Note: In GA4, you can not create custom session-scoped dimensions. GA4 supports three scopes for custom dimensions: event scope, user scope, and item scope.

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How to identify session-scoped dimensions in GA4?

Session-scoped dimensions are always prefixed with ‘Session’ (like ‘Session source/medium’).

That’s how you can easily spot them:

Example of GA4 Session-Scoped Dimension: Session source/medium

Unlike the ‘First User source/medium’ (user-scoped dimension), the ‘Session source/medium dimension’ in GA4 captures each user session’s traffic source and medium.

This means it can change depending on how a user finds your website or app within a particular session.

When combined with various metrics, the “Session source/medium” dimension can offer valuable insights into user acquisition channels, campaign performance, user journey within a session, content and marketing optimisation, and user engagement levels for different traffic sources.

For example, consider the following data table:

We can draw the following conclusions from this data table:

#1 Organic Search (google / organic) drives a significant number of sessions (5,000), suggesting it’s a strong acquisition channel.

#2 The high bounce rate for Facebook social traffic (40%) might indicate a content mismatch between social media ads and landing pages.

#3 Users with direct traffic have the longest session duration and most pageviews, indicating familiarity and deeper exploration within the session.

#4 While driving a smaller audience (500 sessions), ‘Email Marketing (newsletter/email)’ users show high engagement with more ‘pageviews per session’, suggesting they navigate through more content after arriving via an email newsletter. The email traffic also resulted in the highest ‘add to carts’ (400), indicating this channel is most effective at driving users towards the purchase intent stage.

GA4 Session-scoped dimensions vs Attribution

GA4 assigns conversion credit for session-scoped dimensions using the ‘paid and organic channels last-click attribution model’. 

This model attributes the conversion to the last non-direct click from paid or organic channels before the conversion event.

Consider the following user journey:

Session 1 (facebook / referral): A user clicks on a link shared in a Facebook post and browses your website for a while but doesn’t make a purchase (Session source/medium: “facebook / referral”).

Session 2 (google / organic): Later in the day, the user performs a Google search for your brand and clicks on an organic search result, leading them back to your website (Session source/medium: “google / organic”). This time, they complete a purchase.

In this case, the conversion (purchase) would be attributed to “google / organic” since it was the last non-direct click before the conversion event, even though the Facebook post sparked the user’s initial interest.

However, it is important to clarify that session-scoped dimensions themselves do not use a ‘paid and organic channels last-click attribution model’. 

This is because the values of session-scoped dimensions do not change based on user behaviour or the attribution model you choose. They are calculated and sent once per session.

Session-scoped dimensions in GA4 function entirely separately from attribution models.

Session-scoped dimensions are unaffected by changes to the reporting attribution model (you select under Data Display > Attribution Settings):