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

Page: https://alidemirbas.com.tr/en/lab/ab-test-library/tests/moving-the-cta-into-the-mobile-thumb-zone-ab-test

## Hypothesis

If the CTA stays within reach in a fixed bottom bar while mobile visitors scroll, they can add the product the moment they decide, without scrolling back to the button. The add-to-cart rate among assigned mobile visitors should then rise, unless the bar gets in the way of content.

## When to run this test

Mobile product pages where visitors struggle to reach the CTA are where this test belongs: deep scrolling on long pages paired with weak add-to-cart, or recordings of visitors scrolling back up to find the button. The behavior to expect is that visitors who decide further down the page add to cart straight from the bar, and exits do not rise. If they leave over product options, stock or price, look at those first. Before launch, keep the bar below one-third of the screen and clear of bottom navigation.

## Primary metric

**Add-to-cart rate**: Compare successful add-to-cart events per eligible assigned mobile visitor.

## Other metrics

- **CTA click-through rate**: Use 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 rate**: Compare exits in the same session window.

## What to check before and during the test

- **Bar**: Move the existing CTA into one predefined fixed bottom bar.
- **Content visibility**: Keep product information visible and unobstructed; this is an implementation check, not a metric.
- **Trigger**: Set the scroll or visibility rule before launch.
- **Platform**: Review supported mobile platforms separately.
- **Page length**: Read results within page-length groups defined before the test.

## What to watch when reading the result

- CTA click-through rate is a diagnostic, and a raw click gain does not justify shipping. Decide on successful add-to-cart rate, then check that the gain carries through to purchase conversion and that page exit rate does not climb.
- The bar changes visibility and position together, so do not credit the result to thumb reach alone. If you also change the CTA label, you cannot tell which change moved the number; read each supported mobile platform and the predefined long- and short-page groups separately.
- Before you read the result, confirm the rest of the screen stays usable and the bar never overlaps the CTA when the keyboard is open. Visitors should be able to dismiss the bar without losing the main action; otherwise a rise in exits may come from the bar itself.
- An inconclusive result may partly reflect that splitting mobile traffic by platform and page length leaves each group smaller. Enter the current add-to-cart rate and the lift you care about in the [sample size calculator](https://alidemirbas.com.tr/en/calculators/sample-size-calculator) to get the sample needed per variant. Compare that with the traffic each group gets, and decide from there whether to extend the test.

## Frequently Asked Questions

### Does this prove an effect from easier thumb reach?

No. It measures the defined sticky-bar experience, combining placement and visibility. Do not attribute the result to thumb reach alone. Keep CTA wording unchanged.

### Does a higher CTA click rate mean the sticky bar won?

Clicks alone are insufficient. Use successful add-to-cart rate as the primary outcome, with purchase conversion and exits showing downstream effects and possible disruption.

### What if the sticky bar covers product content?

Avoid covering information, fields or controls. Check the keyboard, bottom navigation and device safe areas. Under WCAG 2.4.11, a focused component must not be entirely hidden by author-created content.

### Which visitor groups should I examine separately?

Review supported mobile platforms and predefined long- and short-page groups. The value of the bar may vary with page length. Keep its scroll or visibility trigger fixed.