Ivory Towers: Feeling tired? Are you sure?

FEELING sleepy? How sleepy? And are you really as sleepy as you think you are? Such questions have been keeping psychologists awake in the search for a reliable measure of sleepiness in order to diagnose and treat a variety of sleep disorders.

The latest advance in the field comes from research at the Sleep Disorders Unit at Epworth Hospital, Melbourne, Australia, as reported in two papers, 'A New Method for Measuring Daytime Sleepiness: The Epworth Sleepiness Scale' and 'Reliability and Factor Analysis of the Epworth Sleepiness Scale', both by Murray W Johns and published in the journal Sleep (vol 14, No 6 and vol 15 No 4).

Before the Epworth Sleepiness Scale was developed, there was a variety of ways to measure somnolence. The Multiple Sleep Latency Test, the Stanford Sleepiness Scale, the Sleep-Wake Activity Inventory and the Maintenance of Wakefulness Test all had their disadvantages, either in difficulty of administration or unreliability. The new scale was developed as a quick and reliable alternative.

Sleepiness, for the purpose of this research, is defined as 'the propensity to fall asleep when encouraged to do so in a non-stimulating environment'. Until now, the standard clinical instrument for measuring this has been the Multiple Sleep Latency Test which Dr Johns describes as 'very cumbersome, time-consuming and expensive to perform.

It takes all day, both for the subject and the polysomnographer, and is not easy to justify as a routine test for all patients.' It does, however, measure the propensity to fall sleep in a non-stimulating environment by encouraging the subject to do precisely that, at various times during the day, and measuring how long it takes before he or she nods off. The Stanford Sleepiness Scale, by contrast, is a quick check-list of symptoms of sleepiness.

As such, however, it measures sleepiness at a particular time rather than general sleepiness. 'Nor, it appears, is the subjective sleepiness that they (the Stanford Sleepiness Scale and similar instruments) measure the same as the objective sleepiness measured by the MSLT, even when measured at virtually the same time.' There is a natural confusion between tiredness and the propensity to fall asleep.

The idea behind the development of the Epworth Sleepiness Scale was to ask people not how sleepy they felt, but how likely they thought they were to doze off in a variety of unstimulating situations. Respondents were asked to rate, on a 4-point scale, their dozing potential when sitting and reading, watching television, at the theatre or in a public meeting, as a passenger in a car, lying down in the afternoon, sitting and talking, after an alcohol-free lunch, and in a car stopped in traffic. The points on the scale varied from 0 (would never doze) to 3 (high chance of dozing). With eight situations and scores of 0 - 3 on each, there is a maximum score of 24 on the test, formed as the sum of the individual responses. Only subjects already diagnosed as suffering from sleep disorders scored 16 or more.

'The concept of the ESS was derived from observations about the nature and occurrence of daytime sleep and sleepiness', the author explains. The methodological problem here is that some sleepy people do not sleep during the day, and some people who sleep during the day are not sleepy people. 'Among recruits entering the French army, 19 per cent reported sleeping during the day, regularly or occasionally. But only 5 per cent complained of daytime sleepiness.' The bored, the socially withdrawn and the idle may choose to have naps, while the genuinely sleepy may try to stay awake, deliberately avoiding daytime sleep. The ESS tries to overcome this confusion by letting the subject imagine soporific scenarios.

And it seems to work: 'ESS scores proved capable of distinguishing individuals and diagnostic groups over the whole range of daytime sleepiness.' They also correlated significantly with measures on the Multiple Sleep Latency Test.

Interestingly, scores on the eight items of the test also correlate strongly with each other, indicating that sleepiness is a general trait rather than being context dependent. Everybody is more likely to doze when watching television than when sitting and talking, but those more likely to nod off during Neighbours are also more likely to be bored to sleep by their neighbours' conversations. 'The ESS does not ask how frequently the subject falls asleep while watching television. That would depend on how frequently he watched television as much as on his sleepiness.'

Finally, Dr Johns says: 'The ESS assumes that subjects can remember whether or not and under what circumstances they have dozed off during the day . . . The present results suggest that most patients can give meaningful self reports about this aspect of their behaviour and that their ESS scores provide a measure of their general level of daytime sleepiness . . . This has not been achieved previously by any other published questionnaire. So if you are still awake, thank you for reading.