[coldtea]

That's exactly what the parent says.

"Add it altogether and an "eight hour night" may actually only constitute 6.5 hours of actual physiological sleep. ".

[continuations]

Which is the problem being raised.

According to the study 9 hrs of sleep is bad for your health (too much sleep). But that 9 hrs may actually constitute 8 hrs of actual physiological sleep. So 8 hrs of actual sleep is too much and is bad?