I have sleep this week, and not just because I have lost an hour of this weekend at the summer time.
People in developed countries sleep less than before. In the USA, a 2015 study found that the average age-adjusted sleep duration was 7.18 hours, compared with 7.4 hours in 1985.
That's why the premise of a new study in Nature human behavior is so intriguing. Published this week, the study says having less sleep makes us less prosocial – less inclined to vote, donate money to charity, sign petitions.
The study intrigued me, but I was also wary. I wrote on the replication crisis in psychology researchand this study resembled a study that might not succeed: a broad and striking claim, several different metrics of interest, even the fact that it was published in a prestigious newspaper (some analyzes found that the best journals publish more questionable studies than more domain-specific journals).
In addition, the size of the effects is quite large – often indicating that the results do not stand up to scrutiny. And there is a long history of questionable studies claiming disproportionate effects on the vote, caused by everything from television to menstruation.
I spent some time digging through this sleep research. And as it happens, it's pretty solid.
Some evidence suggests that sleep is important – a lot
Researchers – political scientists John Holbein and Jerome Schafer and economist David Dickinson – Start by observing that survey respondents who report less sleep are less likely to vote. This could easily be confused with dozens of things – most obviously, people probably sleep less because they are busier, which hinders the vote but also most other activities.
The researchers are trying to control this, but the "control of" confounders is not working as well as expected, and the reported effect size is strangely large. A sign of poor statistical methodology in one study is that all findings are just below the statistical significance threshold (that is, the effects found in the study count as statistically significant, but barely), but the problem surprisingly large effects of small changes – is also a sign of statistical malpractice.
I think of this as the rule of psychology studies that studies are psychological – if they claim that wearing red, watching a scary movie or ovulating accounts for 10% or more of the variation in how people vote , eat or behave, there is probably something wrong there. The subconscious effects just should not be as important – and if they are, are there not 10 other such random effects that affect the results?
To manage this, researchers have turned to a methodology that uses discontinuities in the sleep quality of Americans near time zone boundaries. Regression discontinuity analysis can be used to determine causal relationships by analyzing how a variable – in this case, the probability of voting – varies across borders, where the number of people who sleep is limited.
It turns out that Americans living 'in the immediate vicinity of the US Border Zones' side have managed to get 20 to 25 minutes less sleep per night (on average) compared to those living nearby immediately on the west side of the same time. It's a terrifying and surprising statistic – does an arbitrary choice of time really affect us?
A source of finding is a different analysis of the discontinuity of the regression, published in 2017, which explains:
In the counties located on the east side (right) of a time zone limit, the hour of sunset takes place one hour later than in the neighboring counties on the other side of the limit. More generally, daylight is delayed by one hour. … Due to the late emergence of daylight and the biological connection between light of the environment and melatonin production throughout the day, individuals lying down at the end from sunset tend to go to bed later.
(They speculate that prime time television hours could also be linked.)
While people go to bed later when the sun sets and sunrise come later, the hours of work and school do not tend to adapt. This study found that the difference between people slept at 19 minutes. (There was a bigger difference for people who had to start work before 7 am or drop their kids to school before 8 am There was a lot less difference for people with flexible hours.)
This is worrisome, but it's really useful for sleep research – it suggests that we can study the effects of sleep by taking advantage of the quasi-experience data that we have created with our time zones.
This is how the new study examines whether the correlation between sleep deprivation and voting holds up. Their analysis of regression discontinuity shows that, yes, people deprived of sleep are much less likely to vote.
Finally, the authors conducted a randomized controlled experiment, asking respondents to the online survey to conduct an attitude survey either by day or by night. Again, the sleepy group was less likely to intend to vote, sign a petition or give money.
Another obvious objection to the study. Maybe tired people … do less of everything, which is a bit misleading to specifically point out that they make less pro-social activity. The paper also considers the use of the discontinuity regression approach to determine that people who sleep less have more free time and spend as much time relaxing, reading, repairing or working as people who sleep more.
There is a variation of this criticism that, in my opinion, should be taken more seriously: can we be sure that what makes voting, petition signing and money donation difficult when one is deprived of sleep, it is precisely that it is prosocial activities, rather than simply that they need to make important decisions, which we are less likely to do when we are tired? The study does not answer that.
This research builds on previous work on the effects of burnout – I am thinking in particular of research on people's fatigue. less likely to do healthy lifestyle choices. There could be a common cause there. When you're tired, it's harder to get things done that we think are important but do not find the intrinsic motivation. So we are less altruistic and also less good for our future (which, at least for me, feels motivated by the same impulse as altruism).
Does this study have significant benefits? I think there are two. First of all, if you live near a time zone change, move to the west side – or at least take a job with a later start time – if you have a choice. Research suggests that this will dramatically affect your sleep.
For the rest of us, before making a donation decision, or before trying to do something difficult and motivated altruistic, it might be helpful to give priority to a restful rest. If the time of day struck you as hard as it struck me, this week is probably a bad time to evaluate how much you want to budget for a charity.
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