Sleep Heart Health Study

6.6.2.1 Rules for assigning epoch-specific sleep score

Epoch-by-epoch approach: The polygraph record is divided into consecutive segments of equal size (30 s., each termed an “epoch”). Each epoch has assigned a single sleep stage score. The epoch duration is maintained for the duration of the recording.

• When more than one stage is present in an epoch, that epoch is assigned a single stage score reflecting the stage that occupied the greatest portion of the epoch.
• When two stages of sleep are evenly distributed on the epoch, and one of these stages was the same stage as in the preceding epoch, then that epoch will be assigned the same sleep stage as the preceding epoch (*).
• Portions of two epochs may not be combined to create a new epoch.
• When an arousal of <15 sec. occurs within an epoch, the time “in arousal” is not counted when determining the predominant sleep stage time in that epoch.