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Overall study grade as assigned by scorer. These codes reflected the total duration of useable (artifact free, scorable) signals during sleep time across channels, weighing those signals most critical for accurate scoring of respiratory events and staging during sleep time. The Quality Assessment Form for SHHS2 was modified so that the overall quality grade and the signal quality codes were based on signals during sleep time. Since events were only scored during sleep time this provided a more accurate assessment of signal quality during the actual time or scoring. This change would only have affected the quality grade of a small number of studies in SHHS1 where there was a significant amount of time awake with very good signals combined with very poor signals that occurred during sleep. The overall and signal quality grades are comparable between SHHS1 and SHHS2.

Data was lost during the study.

Scorer observed other outlying values.

Data was lost at end of study due to unscorable signals.

Scorer comments on signal quality issues observed.

Scorer observed alpha intrusion on sleep during study.

Due to problems with EEG signals, arousals were ignored in scoring.

Scorer observed periodic breathing for a period of at least 5 minutes during study.

Scorer observed periodic breathing for a period of at least 10 minutes during study.

Data was lost at the beginning of study due to unscorable signals. Variable not used for Sleep Heart Health Study Visit 1 (SHHS1)

Scorer noted that there was a problem scoring arousals.

Data was lost at the end of sleep period because recording ended before wake.

Data was lost at the beginning of sleep period because recording began after sleep onset.

Scorer noted that there was a problem differentiating stage 1 and stage 2 sleep.

Scorer noted that there was a problem differentiating stage 2 and stage 3/4 sleep.

Scorer observed periodic large breaths during study. When very large breaths (one or two) occur periodically (mostly on the inductance channels) between runs of fairly normal breaths for a duration of at least 10 minutes.

Due to signal problems, scorer was unable to reliably assess arousals. The scoring of arousals was determined to be unreliable.

Due to signal problems, scorer was unable to reliably distinguish between apnea and hypopnea events. The distinction between apnea and hypopnea was determined to be unreliable.

Scorer observed unusual sleep staging. This is noted when there is no sleep in any particular stage (eg. no rapid eye movement sleep (REM)).

Due to signal problems, scorer noted that there was a problem scoring respiratory events.

If a respiratory event greater than 150 seconds in duration was observed, scorer has verified that this value is real.

Study was scored sleep/wake rather than with full sleep staging. This assessment is made by the scorer if there is not sufficient quality on EEG leads to do full R&K scoring. (0=no (full scoring); 1=yes (sleep/wake only)) Studies scored as sleep wake have all sleep stages scored using a default of Stage 2 and no arousals are scored.

If Respiratory Disturbance Index (RDI) = 0, scorer has verified that this value is real.