Rounded/square corners - Coop Obs-BYGG website

Last registered on December 10, 2025

View Trial History

Pre-Trial

Trial Information

General Information

Title

Rounded/square corners - Coop Obs-BYGG website

RCT ID

AEARCTR-0017384

Initial registration date

December 02, 2025

Initial registration date is when the trial was registered.

It corresponds to when the registration was submitted to the Registry to be reviewed for publication.

First published

December 08, 2025, 12:42 PM EST

First published corresponds to when the trial was first made public on the Registry after being reviewed.

Last updated

December 10, 2025, 9:18 PM EST

Last updated is the most recent time when changes to the trial's registration were published.

Locations

Country

Norway

Region

Primary Investigator

Name

Ron Kohavi

Affiliation

Contact Primary Investigator

Other Primary Investigator(s)

PI Name

Joachim Furuseth

PI Affiliation

Coop

PI Name

PI Affiliation

PI Name

PI Affiliation

Linowski Interaction Design

Contact Investigator

Additional Trial Information

Status

Completed

Start date

2024-09-11

End date

2025-01-01

Keywords

Behavior, Lab, Other

Additional Keywords

Online, website, user interrface

JEL code(s)

C12

Secondary IDs

Prior work

This trial does not extend or rely on any prior RCTs.

Abstract

Do elements with rounded shapes enhance click-through rates?

This is part of the Trustworthy A/B patterns project described at https://bit.ly/trustworthyABPatterns.

The first replication with Coop was the web site OBS and the trial was approved: https://www.socialscienceregistry.org/trials/17349
This is the second replication that was done on another site called OBS-BYGG.

Consumers frequently encounter digital design elements intended to influence their behavior, from call-to-action buttons to visual cues that guide online decision-making. A recent study published in the Journal of Consumer Research (Biswas et al. 2023) reported that using rounded visual elements increased online click-through rates by 55% in an A/B test—a finding that, if reliable, would have significant implications for marketers, designers, and digital platforms seeking to enhance consumer engagement

We suspect that the paper suffers from the winner's curse and is highly underpowered. See post at https://www.linkedin.com/posts/ronnyk_do-elements-with-rounded-shapes-enhance-click-through-activity-7183554027773734914--ugr/

Paper reference: Curvy Digital Marketing Designs: Virtual Elements with Rounded Shapes Enhance Online Click-Through Rates co-authored by Biswas, Abell, and Chacko (2023)

External Link(s)

Discussion of paper on LinkedIn

The paper: Curvy Digital Marketing Designs: Virtual Elements with Rounded Shapes Enhance Online Click-Through Rates

Trustworthy A/B Testing project page

Registration Citation

Citation

Furuseth, Joachim et al. 2025. "Rounded/square corners - Coop Obs-BYGG website." AEA RCT Registry. December 10. https://doi.org/10.1257/rct.17384-1.2

Sponsors & Partners

Experimental Details

Interventions

Intervention(s)

The add-to-cart button was changed from round to square.
See screen shots at https://www.linkedin.com/posts/ronnyk_experimentguide-replicationcrisis-lowpower-activity-7280353218268708865-whRF/

Intervention (Hidden)

Intervention Start Date

2024-09-11

Intervention End Date

2025-01-01

Primary Outcomes

Primary Outcomes (end points)

Clickthrough rate

Primary Outcomes (explanation)

For each user in the experiment, they are assigned a 1 if they clicked on the add-to-cart button and 0 otherwise (Boolean).
The clickthrough rate is the average over all users of the 0/1/indicator.

Secondary Outcomes

Secondary Outcomes (end points)

Secondary Outcomes (explanation)

Experimental Design

Users who see an add-to-cart button on the website https://www.obsbygg.no/ are randomized into control/treatment.
They're assigned 1 if they (anytime during the experiment) click on the add-to-cart button and zero otherwise.

Experimental Design Details

Randomization Method

The first time a user visits a detail page where the add-to-cart button is shown, they are randomized into one of the three variants: square corners, rounded corners, or slightly rounded corners. The assignment is consistent for all future visits.

For replication purposes, only the rounded corners and the square corners were being investigated, as that was the intervention in the original paper.

Technically, Kameleoon is an A/B testing product that is used to randomize.
It uses a SHA-256 hash function that is applied to each user (based on cookies) to determine their assignment.

Randomization Unit

User

Was the treatment clustered?

Experiment Characteristics

Sample size: planned number of clusters

No clusters

Sample size: planned number of observations

Over 2M for both arms

Sample size (or number of clusters) by treatment arms

Over 1M for each arm

Minimum detectable effect size for main outcomes (accounting for sample design and clustering)

In https://bit.ly/trustworthyABPatterns, we specified that we are looking to run replications with an MDE of 2%. Our calculations indicated that we would need to run for about 12-15 weeks, so we rounded up to 16 weeks to be conservative

Supporting Documents and Materials

Documents

Document Name

Trustworthy A/B Patterns

Document Type

proposal

Document Description

This is the version of our document published at https://bit.ly/trustworthyABPatterns, as it existed on Google Drive on 8/20/2024, before the experiment started.
The key paragraph proposing the replication is:
------------
a. Rounded/square corners – published result that some believe is highly exaggerated. See https://www.linkedin.com/posts/ronnyk_do-elements-with-rounded-shapes-enhance-click-through-activity-7183554027773734914--ugr
Proposed MDE for power calculations on conversion metric: 2%. This is a tough one to estimate, but several practitioners believe this is much closer to zero than to the 17% plus in the paper.
------------

In later versions of the document, after this experiment finished, we lowed the MDE to 0.5%.
See https://bit.ly/trustworthyABPatterns

File

Trustworthy A/B Patterns

MD5: 349e4b5ce82e04ea45a6e93332780685

SHA1: 28a82df45bd60e5b74892801b41f962209e6ca12

Uploaded At: December 02, 2025

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