Single-Variable Testing

Change one variable per arm so the winner is attributable. Otherwise it's a guess.

How to apply it

If you must test combinations, use a multivariate (MVT) design with proper sample size.

Practise it on a real challenge

Hero Test — three things changed at once

A team ships 3 variants of a hero with different copy, color, and image.

More UX laws

• 60-30-10 Rule
• 8-pt Spacing Scale
• Accessible contrast
• Aesthetic-Usability Effect
• Alignment Principle
• Calibrated Trust