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Like other
symptoms, insomnia is measured along self reported dimensions
such as:
- Length
of time to fall asleep;
- Sleep
duration;
- Awakenings
or arousals (number and duration);
- Sleep
depth;
- Restfulness
of sleep;
- Restlessness
of sleep;
- Waking
or daytime consequences of poor sleep.
Many sleep
questionnaires have been developed but a fairly commonly used
one in research is the Pittsburgh
Sleep Quality Index (PSQI). Often in sleep studies, subjects
are asked to rate the quality of their sleep periodically (e.g.
daily throughout an intervention trial) on a sleep
diary or log.
Commonly asked
features of perceived sleep quality on either a sleep history
or a sleep diary or log include:
- How would
you rate your sleep? (very good to very poor)
- How satisfied
are you with your sleep? (very satisfied to not at all satisfied)
- How rested
do you feel? (very rested to not at all rested)
- After
awakening, how clear-headed do you feel?(very clear-headed to
not at all clear-headed)
From the following
questions on a sleep log or diary, it is possible to calculate
variables such as:
- What time
did you go to bed last night? What time did you wake/get up?
Variable = time in bed (TIB)
- How long
did it take to fall asleep?
Variable: sleep onset latency (SOL)
- How many
times did you wake up? How long were you awake?
Variable: wake after sleep onset (WASO)
Total sleep
time can be calculated by taking the reported time in bed
and subtracting the estimated number of minutes to fall asleep
and the minutes awake after sleep onset. Additionally, sleep
efficiency can be calculated as the ratio of the time in bed
to the total sleep time.
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