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Moving the CTA into the Mobile Thumb Zone A/B Test

A bottom action bar can keep the CTA within reach as visitors browse.

  • Product page
  • Add-to-cart rate

Control vs Variant

Where it sits is the variable; the element itself does not change.

Changed
Placement
Page
Product page
Difference
moved

Hypothesis

It also takes up screen space and may overlap content or controls. The comparison measures the defined fixed-bar experience, including its position and visibility; it does not prove thumb reach alone caused the result.

How to run this test

Primary metric

Add-to-cart rate

Compare successful add-to-cart events per eligible assigned mobile visitor.

Other metrics

  • CTA click-through rateUse clicks as a diagnostic measure, not as the purchase outcome.
  • Purchase conversion rate (CR)Check whether any add-to-cart change carries through to purchases.
  • Page exit rateCompare exits in the same session window.

What to check before and during the test

  • BarMove the existing CTA into one predefined fixed bottom bar.
  • Content visibilityKeep product information visible and unobstructed; this is an implementation check, not a metric.
  • TriggerSet the scroll or visibility rule before launch.
  • PlatformReview supported mobile platforms separately.
  • Page lengthRead results within page-length groups defined before the test.

Setup mistakes to avoid

  1. 1Keep the bar below one-third of the screen and check that the remaining area is usable.
  2. 2Do not let the bar overlap the CTA when the keyboard is open.
  3. 3Do not change the CTA label in the same test.
  4. 4Allow visitors to dismiss the bar without removing access to the main action.
  5. 5Keep the bar clear of bottom navigation.