There is a pervasive feeling in our scientific community and widely reported in the media that humans get less sleep than we used to. The narrative is that as a society we have become chronically increasingly sleep-deprived since the halcyon-days of the 1950–60s—one just has to forget the warm comforts of the Cold War and the barbiturate, benzodiazepine and amphetamine epidemics (Rasmussen, 2009).
Certainly, no one can actually reference any high-quality data (Matricciani et al., 2011), but the whole concept simply intuitively ‘feels’ correct. The Ninja is hiding in the room somewhere: we just have to look harder and ignore all evidence to the contrary. Much like Russell’s rhino, however, if the Ninja is really not there it is going to be impossible to prove it (additionally, Ninjas have a reputation for being very good at hiding).
Our research group, for instance, has failed to locate the hidden epidemic. We looked worldwide using a systematic review to identify all previously published nationally representative repeated cross-sectional studies of sleep duration, and found data from 12 countries dating back to the 1960s (Bin et al., 2012). In six countries sleep durations declined, two had mixed evidence (including the United States) and we found another seven countries where sleep has actually increased (including Britain 1961–84).