Segment-based testing reveals how different user groups respond to the same change. While overall test results might show a positive impact, breaking down the data by segments often uncovers important nuances.

Common segments to analyze include:

• Device type (mobile/desktop)
• User type (new/returning)
• Traffic source (organic/paid)
• Geographic location

For instance, a navigation change might show a 10% overall improvement in click-through rate, but segment analysis reveals it's actually helping desktop users (+20%) while hurting mobile users (-5%). This insight helps you make more nuanced implementation decisions.

Testing segments requires larger sample sizes since you're effectively running multiple tests. For meaningful segment insights, each segment needs enough traffic to reach statistical significance. Running segment analysis on small segments like "mobile users from Canada using Safari" often leads to inconclusive results due to insufficient data.