Tuesday, June 19, 2012

Does race or profession affect sleep?

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.

The first was from a few months back at the NYT blog, commenting on the most sleep deprived professions.
The second is from Time magazine, and talks about sleep differences among the races.

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.


  1. I'm just getting tired thinking about it.

  2. Those loggers must be really good at sawing logs...

    Alright, there's not much more to say. Except that reporting small differences as if they were implied big things is standard fare in the news world.

    Unless the narrative they are using insists that the differences aren't important.

    Sometime in the past decade, I realized that the news business is really an entertainment business. Some sort of facts are necessary to have a story to tell, but they are telling a story.

  3. Having been raised by a parent who spent many years logging, I think his input might be relevant here.

    He says "One hour of sleep before midnight is worth two hours of sleep after midnight."

    By his reckoning, if I went to sleep at 9pm and woke up at 4am, I'd be getting the same rest as if I went to sleep at midnight and woke up at 10am. In other words, I'd be gaining 3 hours of rested or useful consciousness.

    I spent several years going to work at 5pm and leaving somewhere between 4am and 7am... usually closer to 7am. I generally got to bed between 11am and noon and was up by 4pm... if I slept at all. At least once a week, I would not sleep for 30 to 48 hours, then might sleep for 12 hours on a day off from work.

    Though it corresponds to no useful sleep/wake cycle, I will stay awake for about 20 hours before wanting sleep... and then I will want about 6 hours of sleep. I don't mind being awake at night or sleeping in daylight -- and I'm sure that's because I don't live in a world ruled by the sun, as my father, in his logging days, did. I can stay awake for 24 to 30 hours occasionally quite easily... and still not want much more than 6 hours sleep.

    Now I think of my grandchildren and their wake/sleep cycles. They are trained... but I've noticed that when it's convenient for their parents to keep them up later, it doesn't make much difference in the wake-up times. The 2 year old normally goes to bed at 7pm and wakes at 7am... but circumstances keep him up until 9 pm and he still wakes up at 7 am and handles his imposed daily routine as well as any other day.

    What happens when the parents try to put that 2 year old to bed at 6 pm? Say they've changed time zones... well, the kid doesn't understand train schedule time zones and he's not going to go to bed "peacefully" until it's 7pm in HIS time zone. He will eventually adjust -- be retrained.

    I can be retrained also. This happens when I'm visiting my grandchildren. I adjust to their time zone and their awake cycles... different ones depending on age.

    But as soon as I am on my own, my preferred 26 hour sleep cycle will assert itself. This is why no one would knowingly want me in to participate in their sleep study :-)