  The power of digital platforms is at the center of major ongoing policy and
regulatory efforts. To advance existing debates, we designed and executed an
experiment to measure the power of online search providers, building on the
recent definition of performative power. Instantiated in our setting,
performative power quantifies the ability of a search engine to steer web
traffic by rearranging results. To operationalize this definition we developed
a browser extension that performs unassuming randomized experiments in the
background. These randomized experiments emulate updates to the search
algorithm and identify the causal effect of different content arrangements on
clicks. We formally relate these causal effects to performative power.
Analyzing tens of thousands of clicks, we discuss what our robust quantitative
findings say about the power of online search engines. More broadly, we
envision our work to serve as a blueprint for how performative power and online
experiments can be integrated with future investigations into the economic
power of digital platforms.
