Brief and distinct empirical sleepiness and fatigue scales.

J Psychosom Res. 2006 Jun;60(6):605-13.

Sally Bailes [a, *] Eva Libman [a, c, e], Marc Baltzan [b, e], 
Rhonda Amsel [e], Ron Schondorfa [e] and Catherine S. Fichtena [d, e]

Affiliations:
[a[ SMBD-Jewish General Hospital, Montreal, Canada
[b] Mount Sinai Hospital, Montreal, Canada
[c] Concordia University, Montreal, Canada
[d] Dawson College, Montreal, Canada
[e] McGill University, Montreal, Canada

[*]Corresponding author. ICFP-Department of Psychiatry, Jewish General 
Hospital, 4333 Cote Ste Catherine Road, Montreal, Quebec, Canada H3T 1E4.

Received 19 January 2005.  Available online 27 May 2006.

This research was carried out at both the Jewish General Hospital and the 
Mount Sinai Hospital in Montreal, Quebec, Canada, with the assistance of a 
grant from the Canadian Institutes of Health Research (number MT-15546).

NLM Citation: PMID: 16731235


OBJECTIVE: Sleepiness and fatigue are conceptually distinct but pervasively 
confounded in research, measurement instruments, clinical settings, and 
everyday spoken language. The purpose of the present study was to construct 
two scales that represent unconfounded measures of sleepiness and fatigue, 
using widely used questionnaires.

METHOD: Four questionnaires purporting to measure sleepiness [Stanford 
Sleepiness Scale (SSS); Epworth Sleepiness Scale (ESS)] or fatigue [Fatigue 
Severity Scale (FSS); Chalder Fatigue Scale (CFS)] were administered, as 
well as a battery measuring sleep, psychological, and health functioning 
variables, to three samples: 19 individuals with chronic fatigue syndrome, 
14 with narcolepsy, and 11 normal control subjects.

RESULTS: Analyses revealed two distinct sets of items (six sleepiness and 
three fatigue items) that were combined into two scales. These newly formed 
scales are only minimally correlated and represent separate constructs that 
have reasonably distinctive patterns of association. Findings were 
replicated and validated in a sample of 128 older individuals complaining 
of daytime sleepiness and/or fatigue.

CONCLUSIONS: We conclude that (a) it is possible to derive empirically 
distinct sleepiness and fatigue scales from existing, commonly used 
self-report instruments, (b) the Empirical Sleepiness Scale is limited to 
the experience of daytime sleep tendency, while (c) the Empirical Fatigue 
Scale is associated more broadly with insomnia, psychological 
maladjustment, and poorer perceived health function. The important clinical 
implication of the new Empirical Sleepiness and Fatigue Scales is in the 
ability to identify "sleepiness which is not fatigue," a construct closely 
related to primary sleep disorders, such as sleep apnea/hypopnea syndrome, 
for which there is both available and effective treatment.