It is the summer of 2023, and Rachel is broke. Sitting in a bar one evening, browsing job ads on her phone, she gets a text message. Researchers doing a study on liver function have gotten her name from the bar’s loyalty program—she’d signed up to get a happy-hour discount on nachos. They’re offering $50 a week for access to her phone’s health data stream and her bar tab for the next three months.
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