# Sticky add-to-cart bar with preselected size: +9.6% CR, inconclusive

- Outcome: Flat / inconclusive
- Page type: Product page (Ecommerce)
- Elements: Sticky add-to-cart bars, Variant, size & option selectors
- Test run by: [Clean Commit](https://liftarchive.com/practitioners/clean-commit/)
- Commentary by: LiftArchive (our analysis, not theirs)
- Original source: https://cleancommit.io/ab-tests/sticky-top-add-to-cart-bar-with-size-selector/
- Page: https://liftarchive.com/test/cleancommit-sticky-top-add-to-cart-bar-with-size-selector/

A sticky add-to-cart bar with a size dropdown and a preselected size showed a 9.6% conversion rate lift on mobile, but the result was not statistically significant, so we treat it as inconclusive. Clean Commit ran this test for an anonymized Shopify store and published it in its A/B test library. The targeted metric, add-to-cart rate, rose only 2.2%.

## Result

**+9.6% CR, inconclusive**

- Conversion rate: +9.6% and orders +8.3%, but neither reached significance.
- Add-to-cart rate: +2.2%, with only a 65.8% probability of beating the original. Inconclusive.
- Average order value: -6.9%, so revenue per visitor rose just 2.3%.
- Bounce rate: -10.4%, a sign shoppers stayed on the page longer.

## Control

Mobile product pages had no sticky bar. Shoppers scrolled back to the main size picker and add-to-cart button.

## Variant

A sticky bar stayed on screen with a size dropdown, a 'Find my size' link and a size preselected where possible, so the button was always active.

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

- Keeping size and the buy button in reach removes a scroll back up, which may explain the lift in orders.
- A preselected size makes the button work on first tap, but some shoppers may add the wrong size, which can raise returns.
- The quick path may lead to single-item orders, which fits the drop in order value.

## Caveats

Not statistically significant: add-to-cart had a 65.8% probability of beating the original. Sample size and duration were not shared, and order value fell 6.9%.

## How to run this test

- Hypothesis: If we add a sticky mobile bar with a size dropdown and a preselected size, then more shoppers will add to cart because they can buy without scrolling or picking first.
- Primary metric: Mobile add-to-cart rate
- Guardrail: Average order value
- Guardrail: Revenue per visitor
- Guardrail: Return rate for wrong size
- Who should test it: Apparel and footwear stores with long mobile product pages. Be careful with size preselection if wrong-size returns are costly; you may prefer to require a choice.

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Credit: Clean Commit ran this test and owns the result. Summary and commentary by LiftArchive (https://liftarchive.com/test/cleancommit-sticky-top-add-to-cart-bar-with-size-selector/).
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.