Dataset for "Interoperability Benefits Platform Users: Experimental Evidence of Market Contestability and Multihoming"

We study how interoperability affects user welfare in an online experiment where users choose between joining an incumbent platform, a higher-quality entrant platform, or multihoming. Without interoperability, users often settle into inefficient equilibria where they singlehome on the low-quality incumbent. Introducing interoperability in small groups (of 4 users) does not affect the tendency to multihome but increases adoption of the high-quality entrant, leading to a significant increase in consumer surplus. In larger groups (of 8 users), multihoming is significantly more likely without interoperability, but we observe no significant difference in consumer surplus between the treatments with and without interoperability. Our findings suggest that interoperability facilitates transitions out of Pareto-dominated equilibria by reducing the risk of losing access to the network when switching to a new platform. These results contribute to the policy debate on mandated interoperability for digital platforms, offering evidence that targeted technical interventions can remedy coordination problems.