A new approach to the construct of alertness

There are no psychometric measures to evaluate the critical construct of alertness. We, therefore, developed two questionnaires to measure alertness, the Toronto Hospital Alertness Test (THAT) and the ZOGIM-A, and evaluated their psychometric properties.

We examined the correspondence between scores on the THAT and the ZOGIM-A in a sample of sleep clinic outpatients (n=96) with Maintenance of Wakefulness Test (MWT) results after an overnight sleep study, physiological sleep parameters, measures of subjective sleepiness, and two psychosocial variables (psychological well-being and emotional distress). Test-retest reliability was estimated based on responses from an independent sample of 295 sleep clinic outpatients who completed the instruments before and after an overnight sleep study.

High values were observed for both the THAT (r(tt)=.79) and the ZOGIM-A (r(tt)=.70). Internal consistency reliability (coefficient alpha) was also high: .96 for THAT and .83 for ZOGIM-A. Although neither of the new scales correlated significantly with measures derived from the MWT or nocturnal physiological measures, the two alertness scales did correlate significantly and as hypothesized with subjective measures of sleepiness and other psychosocial measures.

These results support the perspective that subjective alertness cannot be reduced to the absence of sleepiness and corroborate the psychometric adequacy of the THAT and the ZOGIM-A as unique indices of alertness that complement objective data obtained via MWT and physiological indices of sleep architecture.