Figures & data
Figure 1 Decision tree for defining the rest interval.
Notes: (A) Bedtime criteria and (B) rise time criteria.
Abbreviations: A, activity level; L, light level; M, event marker; W, wake.
Abbreviations: A, activity level; L, light level; M, event marker; W, wake.
Table 1 Rest interval: intraclass coefficients between default scoring and scorers (upper panel) and intraclass coefficients between two scorers (lower panel)
Figure 2 Examples of default setting issues.
Notes: (A) Incorrect detection of a rest interval (indicated by arrow) when Actiwatch 2 was not being worn by the participant. (B) Default rest interval set too early (arrow). According to the manual detection rules, the rest interval would coincide with the event marker, since the epochs before the marker showed low-level activity, which may suggest quiet sitting or reading. Light level was zero, which may suggest the Actiwatch 2 light sensor may have been covered (by pyjama sleeve or bedding). (C) True rest interval (arrow) not detected by default setting.
Figure 3 Examples of participant-related issues.
Notes: (A) Event marker and light level do not correspond with the expected drop in activity (arrow). The event marker, usually used to mark bedtime, in this case, will be ignored given the high level of activity that followed. Drop in activity reflects more reliably the behavior of retiring to bed. Thus the epoch that followed a drop in activity would be taken as the start of the rest interval, when a discrepancy of >10 minutes exists between light and event indicators. The second event marker in the record that coincided with increased activity and light level should be marked as the end of the rest interval. (B) Event marker not pressed at bedtime (arrow). Light remained high (it is possible that the participant had dozed off with lights on or slept with a bed light or room partner who might still be awake with the light on). Light then fell to zero (the participant may have awakened later to turn the lights off, or the parent of the adolescent had turned off the light). In this example, the significant drop in activity marked the rest interval (depicted by the light blue), and the sleep period (medium blue) fell within the rest interval. An event marker was placed where it coincided with an increased light level (intermittent in nature). The rest interval should have been ended as depicted by the event marker. (C) A drop in light level to zero is insufficient to mark bedtime, since the activity level remained high (rightward arrow). The epoch that coincided with the drop in activity level was selected as the start of the rest interval, as was correctly identified by the default algorithm. The downward arrow in the record should be marked as the end of the rest interval, where there was an increased level of both activity and light with a solid actogram red bar. (D) At the end of sleep period (arrow), increased activity preceded the increase in light level. The increased activity level, which coincided with the event marker, should mark the end of the rest interval (default algorithm incorrectly marked the end interval).
Figure 4 Examples of inter-scorer issues.
Notes: (A) At the start of the rest interval, light dropped to zero (first arrow), later the light level picked up again (second arrow). Scorers may select either epoch to mark the start of the rest interval. In this case, the drop in activity level together with the event marker should mark the start of the rest interval. (B) Event marker pressed more than once. As shown by the red arrow, the event marker was pressed three times, at 22:08, 22:11, and 22:15. Since scorers may choose to begin the rest interval at any of the three times, it would be suggested in such a case that the last of the three markers should be selected for marking the start of the rest interval.
Table 2 An example of an event diary