Analysis
Segment
Also called audience slice.
Segment is a saved subset of sessions or users defined by rules. You apply it to a report to see only that group.
How it is measured
A segment is a set of conditions, such as device is mobile and country is Canada. It may be session-based or user-based, and the scope changes how conditions combine over a visit or over history.
Check the size of the segment before reading anything. A segment with a few dozen sessions yields rates that swing wildly. Compare it with the whole to make sure the rules selected what you meant.
Worked example
A used-car dealer defines a segment: sessions that viewed three or more vehicle pages and used the finance calculator. It captures 362 of 9,800 sessions over the last 28 days.
That group requests a test drive at 8.8 percent, compared with 1.4 percent for everyone. The dealer places the calculator higher in the page. The segment also shows what the average hid.
How it differs
A segment is a saved subset you can toggle on a report. A filter removes data by rule, sometimes for good. Segments are reversible; permanent filters often are not.
Common errors
Building a segment from too few sessions. Confusing session-scope with user-scope. Forgetting to remove it before sharing numbers. Naming segments with unclear titles. Overlapping segments counted as separate people.
In practice
Create two segments you will use every week and name them by their rule. Check the size each time. Never quote a segment number without the size.