When a store visit happens, the data is validated through a panel of users who volunteer to participate in Google Opinion Rewards. How many users volunteer?

The correct answer is 5 million because Google relies on a vast, global panel of opt-in users to maintain the high statistical accuracy and privacy standards required for reporting store visits. By leveraging the feedback of over 5 million volunteers through the Google Opinion Rewards program, the system can confirm physical presence at a location to calibrate and validate the background signals—such as GPS, Wi-Fi strength, and Bluetooth—used by its machine-learning models. This large-scale human verification process ensures that the extrapolated store visit data provided to advertisers is both representative of real-world consumer behavior and highly reliable for measuring the offline impact of digital ad spend.