SWP: Figure 6 presents the day-to-day error of SWP
for a single representative user. Three days are shown to have
noticeably larger errors than the rest - the 3rd, 5th and 6th
days. On the 3rd day, we find the user forgot to inform SWP
when sleep began, this error is only corrected by the user in
the middle of the night. Later in the week - on the 5th day
- we find the user stopped the app because the phone had
become very hot. Finally on the 6th day, the user reports thephone shifted position during the night and by the morning the
phone was far from their pillow; this limited the accelerometer
from accurately detecting the movement (and therefore waking
periods) of the person. Collectively, these problems reflect
the sensitivity of SWP to the user complying with the usage
protocol. Additional reasons for non-compliance may include
people with health concerns regarding keeping a phone close
to them at all times.