[GIFtheory]

I think the conclusion is that /total sleep time/ is actually very accurate, while deep/light/rem measurements are crap.

[2devnull]

All they have to do is measure time in bed, which for most people most of the time will correlate closely with total sleep. Insomniacs are outliers so you don’t need to worry about measuring them and most are taught to just get up when they awaken anyway.