Most people are familiar with the concept of a placebo, where merely providing positive information can improve perception of well-being. Yet the opposite also occurs, with negative data making people feel worse about their own health.
That’s a nocebo — Latin for "I shall harm” as opposed to "I shall please” for placebo. And there’s a good chance you have a nocebo strapped to your wrist.
A wave of health-tech gadgets — from fitness trackers to Apple Inc.’s Watch — means hundreds of millions of people are hooked up to real-time feedback devices. They’re designed to measure your steps, encourage you to exercise more, and give daily updates on your mental and physical health. Apple wants you to "close your rings” — the three colorful circles the Watch uses to monitor your progress — and Garmin Ltd. helpfully tells you when your health is "excellent.”