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.
A paper in the most recent issue of Learning and Individual Differences reports an interaction between an individual’s chronotype (the extend to which you are a morning or an evening person) and the timing of academic activities.
I think this is a potentially important result. It suggests that knowledge of a biologically mediated individual difference might allow us to optimize instruction for different students. From the abstract:
Results indicate a synchrony effect (interaction of time of day and chronotype) in achievement and state motivation. Evening types have worse achievement, lower interest, and lower joy in the morning, but there were no significant associations between chronotype and the outcomes in the afternoon. Since adolescent evening types can learn better and are more motivated in the afternoon, schools should offer more learning opportunities in the afternoon.
A surprising finding published in the most recent issue of Clinical Psychological Science:
Seasonal affective disorder (SAD) is based on the theory that some depressions occur seasonally in response to reduced sunlight. SAD has attracted cultural and research attention for more than 30 years and influenced the DSM through inclusion of the seasonal variation modifier for the major depression diagnosis. This study was designed to determine if a seasonally related pattern of occurrence of major depression could be demonstrated in a population-based study. A cross-sectional U.S. survey of adults completed the Patient Health Questionnaire–8 Depression Scale. Regression models were used to determine if depression was related to measures of sunlight exposure. Depression was unrelated to latitude, season, or sunlight. Results do not support the validity of a seasonal modifier in major depression. The idea of seasonal depression may be strongly rooted in folk psychology, but it is not supported by objective data. Consideration should be given to discontinuing seasonal variation as a diagnostic modifier of major depression.
Here’s one passage from this very interesting paper:
There have been other reports that support this finding and cast doubt on sunlight exposure as a causal factor in depression. Hansen et al. (2008) reported no increase in depression in northern Norway during the twomonth-long “dark period” (p. 121). A large-scale study of residents of Tromsø, Norway, a city north of the arctic circle and also subject to the two-month polar night, found neither an increase in self-reported mental distress during the polar night nor a decrease in reported mental distress during the polar day (Johnsen, Wynn, & Bratlid, 2012).
Two topics that I have interested me for a long time are circadian psychology (how behavior is shaped by circadian rhythms) and hemispericity (the still controversial idea that individual differences in psychology may be related to the brain’s hemispheres).
Here is a paper that ties these to areas together
“Research has shown that thinking styles could have an influence on academic achievement. Previous studies have described that evening types are usually right-thinkers who tend to be creative and intuitive, whereas morning types tend to be left-thinkers who prefer verbal and analytic strategies in processing information. However, these studies have been realized among undergraduates, who have more freedom to choose their time schedules according to their circadian preference than adolescents or adult workers. On other hand, the relationship between thinking styles and circadian preference has not been analyzed considering school achievement. The present study aims (1) to investigate the relationship between circadian preference, that is, behavioral differences in circadian rhythmic expression, and thinking styles, referring to the preference toward information processing typical of the right versus the left cerebral hemisphere; and (2) to test the implications for self-reported school achievement. A sample of 1134 preadolescents and adolescents (581 girls; mean ± SD age: 12.1 ± 1.47, range: 10–14 yrs) completed the Morningness-Eveningness Scale for Children (MESC) as measure of circadian preference (morning, neither, or evening types), the Hemispheric Preference Test (HPT), conceived as a tool to measure thinking styles (right-, balanced-, and left-thinkers), and self-reported school achievement. Results indicated a greater percentage of left-thinkers among morning types and a greater percentage of right-thinkers among evening types. No differences were found among balanced-thinkers and neither types. Morning types and left-thinkers reported the highest subjective level of achievement, followed by evening types and left-thinkers, and morning types and right-thinkers. Evening types and right-thinkers reported the lowest subjective level of achievement. Finally, multivariate regression analysis indicated that age, left hemisphere and morning preferences accounted for 14.2% of total variance on self-reported achievement.”
A story in Vox about 69 year old chronobiologist Robert Sothern’s daily recording of his own vital signs. Something he has been doing for decades:
“I measure my heart rate for a minute,” he tells me on a recent phone call. “I measure blood pressure. I measure respiration for two minutes, breathing slowly and counting how many times I inhale. I measure peak flow [air flow from the lungs], and I’m doing time estimation [counting to 60 without looking at the clock, and then seeing if it matches].” Fourteen years ago, he started to wear a step tracker.
Sothern notes the appearance of cycles in his data:
“We are rhythmic creatures,” Sothern, says. “You look at this … data [and] you can see 10-year cycles in it. You can see daily cycles. You can see even men have something approaching a 28-day cycle in their beard growth — which I did measure for three years too. By having a rhythm, it proves that you are alive.”
Check out Goolge Scholar to see some of his reasearch