In policy discussions about education in developing countries, one neglected topic is the time of day at which the sun sets, something that is determined by arbitrary clock conventions and that can vary considerably both across and within countries. This column reports evidence that discrepancies in the time at which the sun sets across various locations can generate long-term differences in children’s sleep, which in turn influences the geographical distribution of educational attainment. Policies on time zones, school start times, and social protection all have the potential to improve educational outcomes.
Education offers a wide range of benefits that extend beyond increases in labor market productivity. Improvements in education can lower crime, improve health, and increase voting and democratic participation. Therefore, improving educational outcomes for the 40% of the world’s population that are under the age of 25 is one of the foremost challenges for policy-makers.
In policy discussions to this end, one neglected influence is the time of day at which the sun sets, something that is determined by arbitrary clock conventions and can vary considerably both across and within countries.
Each evening the sun sets more than 90 minutes later in West India than in East India. This is because time across the whole country is set to Indian Standard Time. In China, all clocks are set to Beijing Time, which means that the sun sets three hours later in the west than in the east. The sun sets at least an hour later in Madrid than in Munich because Franco’s Spain switched clocks forward one hour to be in sync with Nazi Germany in 1940, even though Spain is geographically in line with the United Kingdom, not Germany.
Similarly, for various historical reasons, clocks in many places—including Algeria, Argentina, France, Russia, Senegal, and South Sudan—are set ahead of their (solar) time and see the sun set later in the day. My research provides the first evidence that by generating large discrepancies in the time at which the sun sets across locations, these arbitrary clock conventions help to determine the geographical distribution of educational attainment levels.
School-age children in locations that experience later sunsets attain fewer years of education due to the negative relationship between sunset time and sleep, and the consequent productivity effects of sleep deprivation. People who are not in poverty adjust their sleep schedules when the sun sets later; sunset-induced sleep deficits are most pronounced among the poor, especially at times when households face severe financial constraints.
Because education is both a driver of economic growth and a means to reduce income inequality, these results imply that sunset time associated with geographical location may contribute to persistent poverty and worsening inequality.
Sunset time, sleep, and education production
As the sun sets and the sky grows darker, the human brain releases melatonin, a hormone that facilitates sleep. Yet social norms or policy choices at the federal or state level—for example, start times for school and work—may dictate wake-up times that do not vary with the time of sunsets. As a result, children sleep less in locations with later sunsets. If sleep is productivity-enhancing, later sunsets may have an adverse effect on learning.
But the effect of later sunsets on educational attainment is ambiguous, and how children trade-off sleep with other time uses may have multiplicative or compensatory effects on education. If sleep makes study effort more productive, a later sunset may not only reduce sleep, but also make studying less effective—therefore decreasing study time.
Conversely, a later sunset (more daylight after school) might make it easier for children to study on their own in the evening, especially in lower income countries where electricity access is intermittent.
Children exposed to later sunset sleep less, study less, and attain fewer years of schooling
Analysing data from the 1998–99 Indian Time Use Survey, I find that an hour delay in sunset time reduces children’s sleep by roughly 30 minutes. When the sun sets later, children go to bed later. By contrast, wake-up times are not regulated by solar cues.
Sleep-deprived children have lower productive effort: later sunset reduces students’ time spent on homework or studying, while increasing time spent on indoor leisure for all children. This result is consistent with the idea that sleep enhances productivity and increases the marginal returns to study effort for students.
Next, I examine the long-run effects of later sunset on children’s academic outcomes. I use nationally representative data from the 2015 India Demographic and Health Survey (DHS) to estimate how children’s educational outcomes co-vary with annual average sunset time across eastern and western locations within a district.
I find that an hour delay in annual average sunset time reduces years of education by 0.8 years. School-age children in geographical locations that experience later sunsets are less likely to complete primary and middle school, are less likely to be enrolled in school, and have lower test scores.
Comparing India, China, and Indonesia
To show that these results are generalizable, I first look at data from China. Making use of variation in annual average sunset time across districts within a state, I find that an hour delay in annual average sunset time reduces children’s sleep by roughly 30 minutes. This is in line with my estimates for India.
To corroborate the effects of later sunset on children’s academic outcomes, I use the 2003 Indonesia DHS, employing a research design based on time zone boundaries in Kalimantan, Indonesia. I find that an hour delay in annual average sunset time reduces years of schooling by 0.7 years. Again, this is similar to my estimate for India.
Poverty helps explain why families fail to adjust their sleep schedules on later sunset days
The timing of natural light is determined by time zones and is therefore predictable across locations and seasons. If sleep is important for productivity, why don’t households adjust their sleep schedules in response to later sunset. Could they simply get on a consistent sleep schedule regardless of sunset time, minimising the resulting effects on human capital? Or do financial or psychological considerations associated with poverty help to explain why families fail to adjust their sleep schedules when the sun sets later?
To address these questions, I examine the diverse impacts of a later sunset on sleep by correlates of poverty (such as education and average monthly expenditure) in India. The negative effect of a later sunset on sleep is at least 25% larger among households of low socioeconomic status.
To evaluate whether this difference truly reflects the influence of poverty, I restrict the sample to crop cultivator households, and make use of variation in wealth around the harvest period. I compare the effect of a later sunset on sleep in the month before harvest, when crop cultivator households are poorer and cash-strapped, with the month after harvest, when they are richer and more financially liquid.
For individuals with formal morning start time constraints—school-age children from crop cultivator households—pre-harvest poverty explains about a quarter of the effect of later sunset on sleep. But for individuals that don’t have formal work start time constraints—adults from crop cultivator households—the entire effect of a later sunset on sleep is driven by the period when the household is poor, before the harvest.
Policy options: Time zones, later school start times, and social protection programmes
Back-of-the-envelope estimates suggest that India would accrue annual human capital gains of over US$4.2 billion (0.2% of GDP) if it switches from the existing time zone policy to the proposed two time zone policy: UTC+5 for Western India and UTC+6 for Eastern India. But there may be benefits associated with the synchronization of daily schedules across the country, and one must be cautious about proposing changes to the existing time zone policy without a thorough cost-benefit analysis.
Therefore, I also explore two other policy interventions that may mitigate the effects of a later sunset on children’s educational outcomes: one is later school start times; the other is social protection programmes.
I find suggestive evidence that later school start times allow children to compensate for later bedtimes by waking up later and attenuate the effect of later sunset on schooling outcomes. Meanwhile, each additional year of exposure to India’s conditional cash transfer programme (MNREGA) mitigates the effect of a later sunset on children’s test scores by roughly 5%.
A version of this column first appeared on the World Bank Blog.