> ## Documentation Index
> Fetch the complete documentation index at: https://docs.abtestly.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Segments

> Narrow the whole results report to a slice of your traffic. Mobile-only, US-only, paid-search-only. Sample size shrinks; the verdict stays honest.

The results page always shows every visitor in the test. Sometimes the
question you really want to answer is narrower: "does the winner still
win on mobile?" or "is the lift real for paid traffic or is it
organic?"

Segments narrow the whole report to that slice.

## Adding a segment

On the results page, click **Add segment**. Pick a dimension and a
value. The rest of the page recomputes, verdict, per-variant
performance, confidence chart, speed panel, for the filtered slice.

You can add multiple segments; they combine with AND. "Mobile" plus
"United States" gives you mobile US visitors only.

The filter also shows up in the URL. Copy-paste the URL into Slack and
your colleague sees the exact same slice.

## The dimensions

* **Device**, Desktop, Mobile, Tablet.
* **Browser**, Chrome, Safari, Firefox, Edge, Opera, others.
* **Operating system**, Windows, macOS, iOS, Android, Linux, others.
* **Country**, pulled from actual traffic on this experiment; countries
  with no visitors do not appear in the picker.
* **New vs returning**, 30-minute session gap.
* **Traffic source**, direct, organic, paid, social, referral, other.
* **Entry path**, the first URL the visitor landed on, bucketed.
* **UTM campaign**, pulled from actual traffic (data-driven picker).

## What "the whole report" means

When you filter, everything on the page recomputes for the filtered
slice:

* Visitors count is the count *in the segment*.
* Verdict, primary metric, guardrails, all recomputed on segment-only
  data.
* Confidence chart plots the segment's history.
* Speed panel shows the segment's speed data.
* Segments cascade, if you filter by Mobile and then by US, the
  visitor pool is mobile US visitors, not mobile OR US.

## Sample size shrinks

A test with 100,000 total exposures filtered to "France, tablet"
might have 300 exposures. The verdict copy honors that, a segment
that lacks the volume for a call says so, even if the whole test has
a clear winner.

## What to do with a segment win

A finding like "variant B loses overall but wins on mobile" is real
information, but it is not a license to ship the variant to mobile
only. Two reasons:

1. **Segment sample sizes are smaller, so segment verdicts are less
   reliable.** A confident segment finding on 300 visitors is less
   trustworthy than the overall finding on 100,000.
2. **You did not pre-register the segment.** The p-value on a
   post-hoc segment is inflated relative to a segment you named
   before the test began.

Take the finding as a **hypothesis** for the next test, not the answer
to this one. "Mobile visitors might respond to B" is a great next
experiment; "ship B to mobile now" is jumping the gun.

## Segments and sequential engines

If you are using the sequential engine, segments still get an
anytime-valid confidence sequence, you can peek at segment results
as often as you like without inflating the false-positive rate.
Frequentist segment reads have the usual multiple-comparisons caveat.

## Live-shareable URL

Every segment filter serializes into the URL as `filter.<dim>=…`
parameters. That means:

* Share a slice in Slack, colleague sees the same view.
* Bookmark a slice, comes back with the filter applied.
* Post in a doc, the reader jumps straight to the slice, no clicking.

## Data-driven pickers

Country and UTM campaign values are pulled from the traffic this
experiment has actually seen. If your test has zero visitors from
Brazil, Brazil does not appear in the picker. That prevents "the
filter that filters everything out" as a class of confusion.