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questionnaire composed of eight questions to measure the general level of daytime
sleepiness in terms of the probability of falling asleep during daily activities: (1) sit-
ting and reading, (2) watching TV, (3) sitting inactive in public place (e.g. a theatre
or a meeting), (4) riding as a passenger in a car for an hour without a break, (5) ly-
ing down to rest in the afternoon when circumstances permit, (6) sitting and talking
to someone, (7) sitting quietly after lunch without alcohol, and (8) sitting in a car,
while stopped for a few minutes in traffic. Each item has a score between 0
3. The
answers are never, slight chance, moderate chance, and high chance. The maximum
score is 24. Typically a score of 11 and above is recognized as excessive daytime
sleepiness (EDS). Thus, the operational definition of daytime sleepiness allows for a
mapping of the concept of sleepiness (in particular context) into an interval between
0 and 24. EDS is defined as a score of ESS
−
11. These definitions are essential for
standardization of meanings and data integration in medical data mining. However,
interpretation of the meaning of a particular ESS value requires thorough contextual
analysis. We describe the main issues of the contextual interpretation in the next
subsection.
≥
13.3.2
Contextual Interpretation of Excessive Daytime Sleepiness
The symptom of sleepiness, although extensively used in screening and diagnosis,
is not easy to describe and, moreover, to quantify. Sleepiness can be measured only
indirectly - there is not yet a single laboratory test to identify 'sleepy' individuals.
However, excessive daytime sleepiness (somnolence) is one of the most important
symptoms of
OSA
used for screening, evaluation, and classification of the severity
of
OSA
[3]. Sleepiness is a typical complaint of
OSA
patients (or their family mem-
bers). But sleepiness is not a universal symptom; about 10% patients with
OSA
do
not display excessive sleepiness. Moreover, reported sleepiness may be related to
many other problems. Figure 13.1 illustrates the complex dependencies between
Excessive Daytime Sleepiness (EDS) and shift work, sleep deprivation, circadian
rhythm disruption (CRD), depression, insomnia, and presence of other sleep disor-
ders such as periodic limb movement (PLM) or restless legs syndrome (RLS). The
arrows represent possible causal relationships between the factors. For example, de-
pression may increase insomnia and, vice versa, insomnia may increase the feeling
of depression.
13.3.3
Operationalization of Obstructive Sleep Apnea
In the case of medical concepts, their meanings are a result of many possible inter-
pretations depending on their context, their specific use, and the particular time of
use. Therefore, modeling of medical concepts must be based on the following four
premises: (1) only some clinical concepts have clearly defined boundaries; most
concepts are fuzzy; (2) clinical concepts are used in specific contexts and are sub-
ject to various interpretations; (3) clinical concepts are created and used for specific
