I’ve commented before on my skepticism about self reported sleep studies.
Two recent studies on sleep piqued my interest, and while my original criticisms hold, there was yet another issue I wanted to bring up.
My gripe with both studies is the extremely small difference between the rankings.
In the professions study (sponsored by Sleepy’s btw), the most sleep deprived profession (home health aide) clocks in at 6hr57m. The most well rested is loggers, with 7h20m. On a self reported survey, how significant is 23 minutes?
From the study on races:
Overall, the researchers found, blacks, Hispanics and Asians slept less than whites. Blacks got 6.8 hours of sleep a night on average, compared with 6.9 hours for Hispanics and Asians, and 7.4 hours a night for whites.
Here we see the same thing….there’s a 6 minute difference between the totals for Blacks and Hispanics and Asians. Whites get 30 minutes more than Hispanics/Asians and 36 minutes more than blacks.
I question the significance of this, since I can’t remember whether I went to bed at 9:00 or 9:30 last night, and would have to guess if someone asked me. Both surveys state this was self reported, and thus the chance these averages could be even closer together is huge.
Additionally, these differences do not actually reach the level of significance that the studies showing the dangers of sleep deprivation reach.
For example, in this study about sleep and overeating, subjects were woken up 2/3rds of the way through their normal sleep time. That would be 2 hours early for nearly everyone above. The studies on heart disease were only linked with chronic insomnia. Cancer and diabetes are both more common in shift workers, but as someone who worked overnights for 3 years, I can tell you that’s not the same as waking up 30 minutes early.
Kaiser Fung has a great post about the popularizing of tiny effects that will be a hit if you didn’t like Freakonomics.