Table 1.

Daily measures of activity and sleep and how they were calculated.

Type of measure	Measure	How it was measured and calculated
Time	Day of study (semester)	Coded as the number of days since the first day of the study.
	Day of week	Ordinal variable coded Monday (0) through Sunday (6).
Sleep	Sleep duration	Longest contiguous time that the participant was not physically active starting after 9 PM.
Activity	Daytime activity	Fraction of time a participant was physically active during the median active period. The median active period is the time between the median hour the participant became physically active during each day of the study and the median hour that the participant stopped being active during the study.
	Nighttime stillness	Fraction of time the phone was predicted to be still, that is, set down, during the median still period. The median still period was calculated over the course of the study to be the median hour that the longest contiguous still period started and the median hour it stopped.