A study in the Journal of Medicine and Pediatrics found that children who used mobile media devices such as smartphones and tablets at bedtime were more likely to have sleeping difficulties, inadequate sleep time and poor daytime function than those who didn't use such devices. The findings were based on pooled data from 20 studies involving 125,198 children ages 6 to 18, and found that among those who had access to a screen device at bedtime at least three times a week, there was an 88 percent increased risk for not getting enough sleep (defined as at least 10 hours a night for children and nine for adolescents), and a 53 percent increased risk of poor sleep quality. Even having an unused device in the bedroom increased the risk for sleep problems. Although this may all sound alarming, the authors acknowledged the studies had limits. All the data was observational and depended on self-reports, which can be unreliable. Also to be kept in mind is that poor sleep habits in and of themselves can lead to increasing use of devices.