Power Analysis is Essential: High-Powered Tests Suggest Minimal to No Effect of Rounded Shapes on Click-Through Rates
Ron Kohavi, Jakub Linowski, Lukas Vermeer, Fabrice Boisseranc, Joachim Furuseth, Andrew Gelman, Guido Imbens, Ravikiran Rajagopal
Stop trusting A/B test results without checking statistical power. Demand power calculations upfront—anything below 80% is noise dressed as signal. Treat viral UX findings with the same skepticism you'd apply to a startup's growth metrics.
A Journal of Consumer Research study claimed rounded buttons increased click-through rates by 55% (p=0.037). The finding went viral in design circles despite a fatal flaw: statistical power below 50%.
Method: Underpowered studies suffer from the winner's curse—any significant result must exaggerate the true effect to cross the significance threshold. The authors ran a high-powered replication (N=10,000+) and found the rounded-corner effect collapsed to near-zero. The original 55% lift was a statistical mirage amplified by low sample size and publication bias.
Caveats: Focuses on button shape; doesn't address whether other micro-interactions suffer from similar replication failures.
Reflections: Which other widely-cited UX findings (e.g., color psychology, whitespace effects) would collapse under high-powered replication? · Should design systems teams require minimum power thresholds before adopting A/B test winners? · How do we build institutional memory when low-power studies dominate practitioner discourse?