# Size Selection in a Bottom Sheet or Inline A/B Test

Page: https://alidemirbas.com.tr/en/lab/ab-test-library/tests/size-selection-in-a-bottom-sheet-or-inline-ab-test

## Hypothesis

On a long mobile product page, if inline sizes sit off screen, the focused bottom sheet panel could make choosing easier. When the sizes are already in view, the extra opening step may become friction instead. Which format pulls ahead on add-to-cart rate with a size selected may depend on where the selector sits on the page.

## When to run this test

Session recordings of mobile shoppers hunting for the size selector or opening and closing the size options over and over, or taps on add to cart before any size is chosen, show that picking a size has become a struggle. If one container suits the page layout better, it lets shoppers finish size selection with less back-and-forth, and add-to-cart follows. If the friction comes from stock information or the size chart, look there first. Check before you start that the sheet has a visible close button, stays within the predefined half-screen limit with every control usable, and keeps the scroll position.

## Primary metric

**Add-to-cart rate**: Compare successful add-to-cart events with a size selected per eligible assigned visitor.

## Other metrics

- **Size selection completion**: Use the same eligible starting population in both arms.
- **Purchase conversion rate (CR)**: Check whether the result carries through to purchases.
- **Size-related return rate**: Track size-related returns over the same follow-up period.
- **Return-to-page usability**: Check that closing the sheet preserves the usable page and prior scroll position.

## What to check before and during the test

- **Container**: Compare the same selector in a bottom sheet and inline on the page.
- **Discoverability**: Keep stock information and size availability unchanged.
- **Access**: Review touch interactions on the targeted mobile layouts.
- **Platform**: Review each supported platform separately.
- **Unavailable sizes**: Keep the same disabled-size treatment in both arms.

## What to watch when reading the result

- The comparison rests on add-to-cart rate with a size selected. Measure size selection completion over the same eligible starting population in both arms; leaving out visitors who never open the sheet flatters that arm. More adds that come with lower purchase conversion or more size-related returns are a warning, not a win.
- Keep the size chart in the same place in both arms, so the result speaks only to the container and does not automatically carry over beyond the mobile layouts you tested. Read each supported platform on its own, and compare size-related returns once orders in both arms are past the follow-up period.
- When the arms come out close, use return-to-page usability and touch interactions to see which arm is causing trouble. Work out how many visitors you need to detect the smallest difference worth acting on with the [sample size calculator](https://alidemirbas.com.tr/en/calculators/sample-size-calculator), and divide that sample per variant by daily mobile traffic per arm to plan the run.

## Frequently Asked Questions

### How can size-selection completion be compared fairly?

Use the same eligible starting population, including users who never open the sheet. Use successful add-to-cart with a valid size as the primary outcome.

### What should be checked in the bottom sheet?

Verify dismissal, focus, preserved selection and return to the expected page position. Keep contents usable on supported screens and unavailable sizes unselectable.

### What matters if add-to-cart improves?

Apply the purchase and size-return guardrails over equal follow-up windows. Inspect supported platforms separately rather than assuming more cart additions become completed sales.