문제 3Wearable devices that track sleep have become enormously popular, promising a detailed breakdown of light, deep, and REM sleep each night. These gadgets typically rely on movement sensors and heart rate monitors to estimate sleep stages, since directly measuring brain activity would require equipment found only in a sleep laboratory. This indirect approach, however, introduces significant uncertainty. Independent studies comparing wearable data with polysomnography, the gold-standard method used in clinical sleep labs, have found that _______________. Some trackers overestimate deep sleep, while others underestimate the amount of time spent in REM sleep, and the margin of error can vary widely between brands. Despite these limitations, many users have come to treat the nightly score generated by their device as an objective medical verdict, sometimes experiencing anxiety when the number falls below what they expect, a phenomenon researchers have begun calling orthosomnia.