BEAT Seminar - Subhasish Chowdhury - (Sheffield) "Default Search Engine Settings and Consumer Switch Behaviour: Results from a Field Experiment"

We study the causal effect of default search engine assignments on user behaviour using a large-scale randomized controlled field experiment. In collaboration with a private browser company, approximately 6,000 new users were exogenously assigned to either Google (control) or Bing (treatment) as their default search engine. Leveraging granular, user-level event data, we track search engine switching and browser retention over time. The results provide clear evidence of a statistically significant default bias: users display substantial persistence with the assigned default, including Bing, despite its substantially smaller baseline market share. Importantly, we show that this default bias is moderated by user quality. More active and highly engaged users are significantly more likely to override the default and switch search engines. We further document pronounced heterogeneity in default effects across demographic and behavioural characteristics, including gender, geography, income, and engagement intensity. This study provides the first experimental evidence quantifying default-induced inertia in the search engine market and offers direct implications for the assessment of behavioural competition policy and regulatory interventions in digital platforms.