Comparisons in GA4 reports
Comparisons let you split a standard report into side-by-side subsets defined by dimension conditions — for example, mobile vs desktop. They are the standard-report counterpart to explorations' segments, but they are simpler, evaluated inline, and limited to dimensions available in that report.
What this means
A comparison is a condition on dimensions (such as device category equals mobile) applied to a standard report, shown alongside other comparisons and the total. You can stack several to see slices next to each other within the same report view.
How they differ from segments
Comparisons live in standard reports and are evaluated inline using that report's available dimensions; they are quick but constrained. Segments live in explorations, support user/session/event scope and sequence conditions, and are far more expressive. If a comparison can't express the slice — say, a sequence of events — that's the signal to move to an exploration with a real segment.
- Comparisons: inline, dimension conditions, standard reports
- Segments: scoped and sequence-aware, in explorations
- Limited to dimensions present in the report
How it appears in analytics and logs
Each comparison column is the report filtered to a dimension condition. If a comparison returns nothing, the dimension may not exist at that report's scope, or thresholding may have hidden small subsets.
Diagnostic use case
Contrast two or more slices directly inside a standard report — device categories, channels, countries — without building a full exploration.
What WebmasterID can help detect
WebmasterID lets you compare first-party slices side by side without third-party cookies or cross-site identifiers.
Common mistakes
- Expecting comparisons to support sequence or scope logic.
- Applying a dimension a report doesn't expose.
- Reading an empty comparison as zero rather than thresholded.
Privacy and accuracy notes
Comparisons aggregate filtered subsets and apply thresholds. They group by dimension conditions, not by identity.
Related pages
- Segments: slicing analytics into meaningful groups
A segment is a saved subset of your data — users, sessions, or events that match conditions — applied to a report or exploration. The crucial detail is scope: a user-scoped, session-scoped, and event-scoped segment of the 'same' condition return different rows, because they include different units. Misreading scope is the classic segmentation error.
- GA4 standard reports overview
Standard reports are GA4's fixed, pre-aggregated reports — grouped into collections like Life cycle and User — that load fast because they read from aggregate tables. Unlike explorations they are not generally sampled, but they apply (other) row grouping and can differ from exploration numbers, which query event-level data with their own scope.
- Secondary dimensions in reports
Adding a secondary dimension cross-tabulates a report by a second attribute — channel by device, page by country. It is the fastest way to add context to a table, but it multiplies row cardinality, which can push rare combinations into an (other) row and increase the chance of thresholding.
- Website observability
Compare first-party slices side by side.
Sources and verification notes
Last reviewed 2026-06-24. Facts are checked against primary/official sources where available; uncertain specifics are marked “Data not yet verified” rather than guessed.