This study just appeared in the journal Psychological Science:
The degree of punishment assigned to criminals is of pivotal importance for the maintenance of social order and cooperation. Nonetheless, the amount of punishment assigned to transgressors can be affected by factors other than the content of the transgressions. We propose that sleep deprivation in judges increases the severity of their sentences. We took advantage of the natural quasi-manipulation of sleep deprivation during the shift to daylight saving time in the spring and analyzed archival data from judicial punishment handed out in the U.S. federal courts. The results supported our hypothesis: Judges doled out longer sentences when they were sleep deprived.
The Monday after the shift to day light savings time is associated with about 40 minutes of lost sleep. Other studies have found an increased number of car accidents on that day. The authors of this study report that sentences are 5% longer than those on comparison Mondays.
An interesting result, although I do have some skepticism about how well confounding variables can be controlled statistically.
An interesting paper about school schedules and student performance, published in The Review of Economics and Statistics, “How the Time of Day Affects Productivity: Evidence from School Schedules.” Here is the abstract:
Increasing the efficiency of the school system is a primary focus
of policymakers. I analyze how the time of day affects students’ productivity
and if efficiency gains can be obtained by rearranging the order of tasks they
perform throughout the school day. Using a panel data set of nearly 2 million
sixth- through eleventh-grade students in Los Angeles County, I perform
within-teacher, class type, and student estimation of the time-of-day effect
on students’ learning as measured by GPA and state test scores. I find that
given a school start time, students learn more in the morning than later in
the school day. Having a morning instead of afternoon math or English class
increases a student’s GPA by 0.072 (0.006) and 0.032 (0.006), respectively.
A morning math class increases state test scores by an amount equivalent
to increasing teacher quality by one-fourth standard deviation or half of the
gender gap. Rearranging school schedules can lead to increased academic
At first this would seem contrary to the evidence that suggests that later school start times seem to benefit students, but the author addresses this:
My study is also related to the school start time literature.
Research has indicated that due to changing sleep patterns
during adolescence, academic gains can be achieved by starting
school later. Carrel, Maghakian, and West (2011) use
random assignment of college classes and find that having one
hour earlier start times decreases students’ GPA by 0.031 to
0.076 standard deviations. Similarly, Dills and HernandezJulian
(2008) find that even when controlling for course
and student characteristics, students perform worse in earlier
classes. Edwards (2012) uses variation in school start times
produced by staggered busing schedules and finds that starting
school an hour later increases test scores by 2 percentage
Some have interpreted the finding that later school start
times increase students’ academic performance as implying
that given a school start time, students perform better
in the afternoon than in the morning (Carrel et al., 2011;
Dills & Hernandez-Julian, 2008). However, this hypothesis
has not been tested empirically. The common conclusion is
that later start times increase students’ achievement because
students are less sleep deprived. However, this says nothing
about how teaching and learning ability change throughout
the day. School start times affect the average learning in a day
but not differential learning throughout the day. Therefore,
the results of this paper and the school start time literature
estimate slightly different effects.
From the journal Psychological Science:
“Both repeated practice and sleep improve long-term retention of information. The assumed common mechanism underlying these effects is memory reactivation, either on-line and effortful or off-line and effortless. In the study reported here, we investigated whether sleep-dependent memory consolidation could help to save practice time during relearning. During two sessions occurring 12 hr apart, 40 participants practiced foreign vocabulary until they reached a perfect level of performance. Half of them learned in the morning and relearned in the evening of a single day. The other half learned in the evening of one day, slept, and then relearned in the morning of the next day. Their retention was assessed 1 week later and 6 months later. We found that interleaving sleep between learning sessions not only reduced the amount of practice needed by half but also ensured much better long-term retention. Sleeping after learning is definitely a good strategy, but sleeping between two learning sessions is a better strategy.”
From the good folks at Ask For Evidence.
‘The NHS Choices website claimed that “People who sleep less than seven hours a day are 30% more likely to be obese than those who get nine hours or more of sleep”. This seemed a little suspect as no data were provided to back up this claim, so I contacted NHS Choices to ask for evidence.’
A paper from PLOS , “Widespread Changes in White Matter Microstructure after a Day of Waking and Sleep Deprivation.”
From the PLOS Blog:
“Neuroscientists from Norway set out to answer this question in their recent PLOS ONE study, examining how a night forgoing sleep affects brain microstructure. Among their findings, sleep deprivation induced widespread structural alterations throughout the brain.”
“My hypothesis,” says first author Dr. Torbjørn Elvsåshagen, “would be that the putative effects of one night of sleep deprivation on white matter microstructure are short term and reverse after one to a few nights of normal sleep. However, it could be hypothesized that chronic sleep insufficiency might lead to longer-lasting alterations in brain structure. Consistent with this idea, evidence for an association between impaired sleep and localized cortical thinning was found in obstructive sleep apnea syndrome, idiopathic rapid eye movement sleep behavior disorder, mild cognitive impairment and community-dwelling adults. Whether chronic sleep insufficiency can lead to longer-lasting alterations in white matter structure remains to be clarified.”
You can find a sleep time calculator here. For the science behind the 90 minute recommendation see this paper.