Students who get higher grades seem to spend a longer time studying. Studying more, however, necessitates sacrificing other activities. What would you give up? Many students answer that they prefer not to forgo hanging out with friends, using Facebook or binging on Netflix – rather, they just cut down on sleep. Perhaps not entirely unsurprising, this strategy might backfire: your sleep duration is also associated with your grades; but sleep deprivation does not only compromise your focus and alertness on the next day: sleep has a critical role in rendering memories stronger and more stable (memory consolidation), thus helping you learn better. This may be especially crucial when you cram material before an exam.
Is the overall result of cutting down on sleep beneficial (longer studying) or detrimental (poorer focus and memory) to your academic achievements? Most studies examining these issues compare different students’ studying and sleeping times averaged across a month or a year, to see whether students with different study-sleep habits also have different grades. Nonetheless, looking at such aggregate data is not ideal, for two main reasons: first, differences in academic performance across students can be explained by a wide variety of other factors in addition to sleep/study time, such as intelligence, socioeconomic status, stress, health and motivation; second, average data wash out the dynamic nature of academic demands and sleep/study choices, which change from day to day.
These issues could be addressed if a study looked at students’ daily fluctuations in sleep, study time and academic performance, so that each student could be compared to herself: does her academic achievements suffer or profit after a night when she has studied more than usual, compared to a night when she has studied less than usual? Three years ago, a team from UCLA and California State University employed this strategy and tracked over 500 students from three high schools over 3 years. Each year, every student kept a daily journal for 10 days, reporting how long they studied and slept and whether they had any academic problems (e.g., not understanding something in class, or performing poorly on homework and tests).
First, the researchers tested the association between study time and academic performance, and found something surprising: when a student studied longer than usual, they had more academic problems the next day. Importantly, the strength of this association was similar across students: smarter students, more motivated students, students from wealthier backgrounds – all did worse on days after they studied more. However, this association did become stronger from year to year, such that seniors had a stronger association between studying longer and performing poorly compared to freshmen.
Why would you have more academic problems on days after you’ve been studying more than usual? You guessed it: the association between studying longer on certain nights and performing more poorly on the following days was explained by decreased sleeping time. Specifically, the researchers found that, across years, the trade-off between study time and sleep time increased: whereas freshmen could study longer on some nights without it affecting their sleep much, seniors made bigger sacrifices on nights when they studied a lot. Thus, when sleeping time was taken into account, the association between study time and academic problems was no longer getting stronger across years (from freshmen to seniors).
Naturally, I’m not recommending that you start studying less. However, these findings do suggest that if you choose to study for long hours, you may want to sacrifice activities other than sleep. This is all the more critical because, even on usual nights, many college students are sleep deprived (in this sense, they are similar to high school students), which might contribute to the association between less sleep and more academic problems. Sweet dreams!
MY TWO CENTS: undeniably, this study has some methodological issues (in case students suspected that this study expected an association between sleep and academic performance, they might have filled in the journals in a biased manner) and statistical issues (no cross validation of the statistical models used, and an odd way of focusing the tests on how associations change across years). Nevertheless, I find this study worth writing about, because my non-scientific impression is that many students’ underappreciate how critical sleep is. Not that I myself need any excuses to sleep in.
CITATION: Gillen-O’Neel, C., Huynh, V.W., & Fuligni, A.J. (2013). To study or to sleep? The academic costs of extra studying at the expense of sleep. Child development, 84(1), 133-142.