Impacts on Other Time Use

Next, I investigate which activities students forgo in order to sleep more. Since I focus on the impacts on middle school students’ academic performance, I also focus on the time use impacts for middle school students. Figure 1.5 presents changes in time use in treatment and control regions for middle school students. On average, middle school students in the treatment region slept an additional 41 minutes and spent 55 minutes less on educational activities after the policy implementation, whereas middle school students in the control region spent 10 more minutes sleeping and 6 more minutes on educational activities. To eliminate possible time trends during the time frame and different month effects, I then examine their time use on other activities with a difference-in-differences estimation that is similar to slightly modified equation (1.1) in the previous section.

Table 1.7 shows the impact of the 40-minute delayed school start time on middle school students’ time use. First, I estimate the effects on six different activities in Panel A. I find that middle school students spent 29.84 more minutes sleeping, including naps, and 13.48 more minutes on non-sleep personal activities, such as having a meal, and they could do that by reducing their time spent on educational activities by 24.54 minutes and leisure by 18.77 minutes. Panel B shows which educational activities are decreased. The main difference in educational activities is decreased self-study in school by 31.79 minutes.20

This reduction stems from the fact that students initially had a self-study period before their first class starts. Since students go to school by 9 AM and the first class starts at 9:10 or 9:20AM after the delay, schools removed the study hall period in the morning so that the first class and time to go home from school were partially delayed compared to delaying the school start time, as shown in Figure 1.1. Another interesting difference is the increased

20 One thing to note is that school class time does not change significantly. Even though there seems to be a 11.93-minute increase in class time, it can be a measurement error, as a class in middle school is 45 minutes and the unit of time use survey is 10 minutes.

time on non-sleep personal activities, which includes having a meal, and this is reasonable because students are more likely to have breakfast when the school start is delayed by 40 minutes and they sleep only an additional 27 minutes in the morning. Because students return home around 20-30 minutes later without changing bed time, students would have lost available afternoon or evening time. Students may have lost leisure time or out-of- school structured study time, such as private or group tutoring or online lectures. However, the estimates on these activities are not statistically significant and should be considered suggestive. Therefore, delayed school start time in Korea increases sleep time at the cost of time spent in self-study.

Moreover, since school start times affect parents as well as children, it is important to understand the implications of these policies for parents. The first spillovers of interests are changes in sleep time, because sleep patterns present the most significant change for children, followed by other activities. These spillover effects are estimated similarly to equation (1.1), but now I include more control variables such as school level, industry, and job classification for parents as well as children and marriage information. The children and marriage information needs to be controlled for, because one’s time use would be affected by other family members.

Table 1.8 shows the spillover impacts of delayed school start time on parents’ sleep duration. Column (1) includes both parents, whereas Columns (2) and (3) only include mothers and fathers, respectively. Column (1) shows that mothers slept 28.97 minutes less than fathers per night on average. However, having a treated child, having more than one kid, and being a single parent do not have a significant effect on parents’ sleep time. On the other hand, having a treated child increased mothers’ sleep time by 20.59 minutes, having more than one child decreased mothers’ sleep time by 8.45 minutes (Column (2)), and being a single parent decreased fathers’ sleep time by 59.33 minutes (Column (3)).

This likely reflects Korean culture, in which mothers take on most of the household production and family care.

Table 1.9 presents the spillover effects on other activities for mothers (Panel A) and fathers (Panel B). In Panel A, all of the estimates are statistically insignificant for mothers, but time spent on market work has the largest magnitudes. Market work includes doing one’s main work, doing side work, taking a rest during work, doing family business without pay, etc. When I focus on the time spent doing one’s main work, even though it is still statistically insignificant, the magnitude increased so that the estimate becomes -19.83, which is close to the opposite of the spillover effect on sleeping. In Panel B, the spillover effect on non-sleep personal activities is the greatest in magnitude, and it is the only single broad category that has a statistically significant impact. Fathers spent 22.33 minutes more in non-sleep personal activities on average. Personal activities are personal maintenance activities such as sleeping, having a meal, engaging in health maintenance, etc. The most plausible interpretation would be the delayed school start time increasing the time spent having a meal with family members. Even though it was unable to estimate the impact on family meals, as 2014 KTUS does not provide the detailed meal code anymore, on average having a meal was increased by 12.64 minutes, and this is significant at the 1% level. The other activities category experienced the second largest impact, among these the bulk of the time change comes from educational activities. Leisure was also decreased by 13.78 minutes, but this is statistically insignificant.