Agreement of visual scoring of sleep stages among many laboratories in Japan: effect of a supplementary definition of slow wave on scoring of slow wave sleep.

The purpose of this study was to elucidate the agreement of visual scoring of all-night polysomnographic recordings among many scores from different laboratories. Ten scorers including the author from different laboratories in Japan scored the same paper recordings of two young male subjects. We calculated the agreement rate for each stage using an epoch by epoch analysis. In both records, the agreement rates for stages 2 and R were high; on the contrary, those for stages 3 and 4 were low. After adding a supplementary definition of high voltage slow wave in deep sleep, we scored the first NREM period of another subject. The mean agreement rate for stage 3 among 10 scorers was significantly higher than those of the two former subjects. However, the agreement for stage 4 did not change so much. This result demonstrates that there is much interrater (laboratory) variability of visual scoring, especially in slow wave sleep. When the result of automatic scoring is compared to that of the visual scoring to evaluate the reliability of automatic scoring, these findings must be considered.