COMPARISON OF A FREQUENCY-BASED ANALYSIS OF ELECTROENCEPHALOGRAMS (Z-RATIO) AND VISUAL SCORING ON THE MULTIPLE SLEEP LATENCY TEST

In a sample of multiple sleep latency test naps following nocturnal po lysomnograms from a group of 13 patients of varying ages and diagnoses , we compared a computer-derived electroencephalographic (EEG) measure (z-ratio) with standard visual sleep stage scoring. In this clinical population, z-ratio scoring agreed with human scorers approximately 80 % of the time when determining sleep versus wake in 30-second epochs. These results show that a single, objectively quantifiable value deriv ed from a single channel of EEG can distinguish between sleep and wake fulness (as defined by Rechtschaffen and Kales) with at least a modera te degree of precision. When refined, the z-ratio method might be of u se as the basis fora new sleep scoring system, particularly where an a ccurate determination of sleep onset is required.