We have all heard a lot about the relationship between good sleep and academic success. When I was in high-school, TV presenters kept advising children to go to bed early on exam nights. But, it is fair to wonder, if there is any scientific evidence to back up such words of wisdom. It is useful to know what aspect of sleep does matter for school grades and what aspect does not.
In this paper, Kana Okano and colleagues in MIT report the story of how they followed 100 undergraduate students for a whole semester. Students were selected from a bigger cohort all of whom had taken the same course in Chemistry. Each selected student was given a FITBIT smart watch which the participating student had to keep “on” for at least 80% time for the duration of the study (i.e., the semester).
What data was gathered? (1) Time of sleep onset, (2) time of waking up, (3) duration of sleep, (4) sleep quality (which is a metric going from 1 to 10 and determined by costum FITBIT algorithm that is not disclosed in the paper), (5) heart rate, (6) daily walked distance, and (7) daily calorie burn.
How was academic performance measured?
Students took, in total, 9 quiz exams and 3 mid-term exams and 1 final exam. Overall score consisted of 25% for the quizs, 15% for each mid-term and 30% for the final exam.
Question 1: was there any correlation between good night of sleep and a given exam’s grade?
Answer: Not at all. Examining across nearly 100 participants in 9 quiz and 3 mid-term exams, there was no correlation between having had a good night sleep and the grade in the exam.
Question 2: was there any correlation between the length of sleep and final overall score?
Answer: Yes! Longer average sleep time was correlated with higher overall score (see Figure 1).
Question 3: Was there any correlation between sleep regularity and final overall score?
Answer: Yes! There was a negative correlation between overall score and standard deviation. That means, the more regularly a student slept during the term, the more likely they were to get a better final score (see Figure 2).