Like most parents, I worry that my child isn't getting enough sleep. Now it turns out that doctors have been warning kids don't get enough sleep for over a century--long before iPads, and texting robbed children of peaceful sleep. What's more, there's no solid scientific basis for pediatricians'   recommendations on the amount of time children need to sleep. That's the word from researchers in Australia. It turns out that children are sleeping less than those in days of old. The researchers, at the University of South Australia's Health and Use of Time Group, found that kids' nightly sleep time declined   by about three-quarters of a minute each year for the period they studied. My daughter was more likely to beg for a few more minutes of Angry Birds before bedtime.That means nowadays my daughter is sleeping about 50 minutes a night less than her grandfather who had to get up to milk the cows at 5:30 am. What hasn't changed is the predictions from health professionals on the consequences of lack of sleep. "This is a sleepless age and more and more... we are turning night into day," one expert said in 1905. Back then, sleep was seen as a way to restore "wearied brain tissue". Children and "clever" children were thought to be most at risk, and most in need of energy-restoring sleep. The words may be different today, but the threats are pretty much the same. Parents are told that children risk mental and physical problems, and even obesity, if they don't get enough sleep. So the Australians looked to see how much sleep kids do need. The answer is the biggest surprise of this study--no one really knows. "There is almost no exact evidence for proper sleep for children," the authors write. Their work was published in the journal Pediatrics. According to the passage,the decrease of children's sleep is     .
a universal phenomenon a social pressure from education because of the invention of iPads pediatricians' lack of responsibility