Sleep habits of healthy young adults: use of a sleep questionnaire.

The pattern of sleep and wakefulness varies widely between individual people and is influenced by many factors. Several reports involving sub jective recording of sleep habits in young adults have been published, with particular emphasis on the duration of sleep (Bousfield, 1940; Lawrence and Shurley, 1970; Webb and Agnew, 1970). However, the variations within such a population and relation ships between the various aspects of behaviour re lating to sleep and wakefulness have not been described adequately. Much of the emphasis in the many sleep laboratories which have been established throughout the world has been on all-night electro encephalogram monitoring. Details of the usual pattern of dreaming and non-dreaming sleep stages have besn described for normal people of different ages and for patients with various physical and psychiatric illnesses (Kales, 1969). Important as such methods are in providing basic information on the nature of sleep and dreams, they do not tell us all we want to know about people's usual pattern of sleep and wakefulness and the factors which in fluence this pattern. For instance, electronic methods used in the laboratory do not tell us at what time our experimental subject usually goes to bed and to sleep at night when he is at home, nor do they tell us how often he dozes during the day, how often he takes sleeping tablets, how he feels about the quality of his sleep, and so on. This information can be obtained by means of detailed subjective reports in the form of either daily sleep charts kept for several weeks or a sleep questionnaire. Such methods of subjective reporting have been used among various occupational groups as well as hospital patients and healthy people of different ages (Lewis and Masterton, 1957; Masterton, 1965 a, b; McGhie and Russell, 1962; Johns, Egan, Gay, and Masterton, 1970). The importance of both subjective and objective methods for describing sleep habits in detail has recently been emphasized (Johns, 1971). The accuracy of subjective estimates of such para meters as the usual delay to sleep onset and the duration of sleep has been measured using objective techniques in the laboratory (Lewis, 1969; Baekeland and Hoy, 1970). There is a significant correlation between these subjective and objective measures, but the former tend to over-estimate the delay to sleep onset and to under-estimate the duration of sleep. This is a definite disadvantage in using sleep questionnaires but does not preclude their use, especi ally in determining the relationships between sleep habits in different groups of people. Monroe (1967) studied groups of'good' and 'poor' sleepers who were healthy young adults selected on the basis of their responses to a sleep questionnaire. The 'poor' sleepers reported usually having longer delays and more difficulty in falling asleep, and they woke up more often during the night than 'good' sleepers. The two groups did in fact have objective differences in the duration of their sleep, number of night awakenings, and the pattern of sleep stages when monitored electronically. Similar studies have demonstrated significant objective differences in the sleep patterns of subjects reporting to be 'long' as opposed to 'short' sleepers (Hartmann, Baekeland, Zwilling and Hoy, 1970; Webb and Friel, 1971). In the present study a sleep questionnaire was given to a relatively homogeneous population of fourth-year medical students at Monash University, Melbourne in 1969 and 1970. This involved 249 students, all of whom were of similar age and daily routine. In this report we shall describe the varia tions in, and the intercorrelations between, the answers given by these students to questions relating to the quality and quantity of their usual sleep. Some of these students took part also in two ad ditional studies of the relationship between levels of adrenocortical activity and sleep habits, and between personality and sleep habits, the results of which will be reported separately. This study forms part of a long-term investigation of normal variations in subjectively reported sleep and the nature of in somnia which is such a common symptom among hospital patients and in the general community (Johns et al, 1970).