# Sticky add-to-cart bar on mobile: +10% conversion, not significant

- Outcome: Flat / inconclusive
- Page type: Product page (Ecommerce)
- Elements: Sticky add-to-cart bars
- Test run by: [Blend Commerce](https://liftarchive.com/practitioners/blend-commerce/)
- Commentary by: LiftArchive (our analysis, not theirs)
- Original source: https://blendcommerce.com/blogs/ab-tests-shopify/10-increase-in-conversion-rate
- Page: https://liftarchive.com/test/pertronix-mobile-sticky-atc/

A sticky add-to-cart bar on PerTronix mobile product pages showed a 10% conversion rate lift, but the result was not statistically significant, so we treat it as inconclusive. Blend Commerce ran the A/B test for the automotive parts brand. Add-to-cart rate also fell 20%, which pulls in the opposite direction.

## Result

**+10% conversion, not significant**

- Conversion rate: +10%, but not statistically significant. Blend reported the trend held over an extended test period.
- Add-to-cart rate: -20%. Fewer shoppers added items, which is a negative signal.
- Cart clicks: +5%. Slightly more visits to the cart.
- Bounce rate: -3%. A small improvement in shoppers leaving straight away.
- Inconclusive overall: the headline lift could be noise, and the metrics disagree with each other.

## Control

The mobile product page had the add-to-cart button only near the top. Shoppers who scrolled down to read reviews had to scroll back up to buy.

## Variant

A sticky add-to-cart bar stayed on screen as shoppers scrolled, with a second button to view product details.

## Why it likely came out this way (our reading)

- Keeping the buy button in reach removes the scroll back up after reading reviews, which should help shoppers who are ready to buy.
- The details button may have pulled some shoppers into reading more before adding, which could explain the drop in add-to-cart.
- Automotive parts often need fit checks, so the buying decision may depend more on product data than on button placement.

## Caveats

The result did not reach statistical significance despite an extended run, and add-to-cart rate fell 20%. Sample size and exact duration were not shared. Blend still shipped the variant.

## How to run this test

- Hypothesis: If we add a sticky add-to-cart bar on mobile product pages, then more shoppers will buy because they will not need to scroll back up after reading reviews.
- Primary metric: Mobile conversion rate
- Guardrail: Add-to-cart rate
- Guardrail: Revenue per visitor
- Guardrail: Return or cancellation rate
- Who should test it: Stores with long mobile product pages where reviews or specs sit far below the buy button. Plan for enough traffic to reach significance, since this test did not.

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Credit: Blend Commerce ran this test and owns the result. Summary and commentary by LiftArchive (https://liftarchive.com/test/pertronix-mobile-sticky-atc/).
Usage: Free to use, quote and build on, with credit and a link: name the practitioner or organization that ran the test and link to its LiftArchive page. The results belong to the practitioners who ran and shared them; the summaries and commentary are LiftArchive's.