Sleep Problems in Adolescence DIANNE N. MORRISON, B.A., P.G.D.A., ROB McGEE, PH.D., AND WARREN R. STANTON, PH.D. Abstract. A sample of 943 adolescents from the general population were questioned about sleep problems. A quarter of the sample reported needing a lot more sleep than they previously had, and 10% of the sample complained of difficulty falling asleep. Adolescents reporting sleep problems showed more anxious, depressed, inattentive, and conduct disorder behaviors than those who had no (or only occasional) sleep problems. Sleep problems, particularly multiple problems, were associated with DSM-1/1 disorder. There were no significant differences between male and female adolescents on any of the above measures. Finally, sleep problems were relatively persistent over time from ages 13 to 15. J. Am. Acad. Child Adolesc. Psychiatry, 1992, 31, 1:94-99. Key Words: sleep, adolescence, DSM-lll disorder.

Sleeping difficulties are experienced by a significant number of adolescents (Kirmil-Gray et al., 1984), although, as yet, knowledge of adolescent sleep behavior remains incomplete (Strauch and Meier, 1988). Adolescents often complain of tiredness, and it seems that they have an increased need for sleep at this age. Sleep disturbances and daytime sleepiness may be related to anxiety states, psychosocial stress, and affective disorders (National Board of Health and Welfare, 1988). DSM-III (American Psychiatric Association, 1980) lists four groups of sleep and arousal disorders: 1) disorders of initiating and maintaining sleep; 2) disorders of excessive somnolence; 3) disorders of the sleep-wake schedule; and 4) dysfunctions associated with sleep, sleep stages, or partial arousals (parasomnias). Many adolescents report at least occasional difficulties falling or staying asleep. Kirmil-Gray et al. (1984) asked 277 students aged between 13 and 17 years to complete a questionnaire about their patterns of sleep and found that 11% of the students were chronic poor sleepers; 23% slept poorly occasionally, and 66% were good sleepers . Approximately 13% of Price et al.'s (1978) adolescent sample aged 15 to 18 years reported chronic and severe sleep disturbances, and occasional sleep disturbance was reported by approximately 38% of the sample. Both studies found that female adolescents reported more sleeping problems than did male adolescents. However, Marks and Mon-

Accepted July /7, 199/. From the Dunedin Multidisciplinary Health and Development Research Unit, Department of Paediatrics and Child Health, Medical School, University of Otago, Dunedin, New Zealand. The DMHDRU is supported by the Health Research Council of New Zealand and involves several departments of the University of Otago. Much of the data have been collected by voluntary workers from the local community. We are indebted to the many people and, in particular, to the adolescents and their parents, whose valuable contributions continue to make this ongoing study possible. Collection of the mental health data at Phase 15 was partially supported by U.S.P.H.S. Grants 1-23-MH42723-01 and l -ROI-MH43746 from the Antisocial and Violent Behavior Branch ofthe U.S. National Institutes of Mental Health. We acknowledge the help of Dr. P.A. Silva in preparing this report. No reprints available. 0890-8567/92/3101-094$03.OO/O© 1992 by the American Academy of Child and Adolescent Psychiatry.

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roe (1976) found that adolescent boys were more often referred for sleeping difficulties than girls. More recently, Bearpark and Michie (1987) surveyed 350 school children, aged 10 to 17 years, to ascertain the prevalence of various sleep and wake disturbances. The most common problem was trouble falling asleep, reported by approximately 23% of the sample. Reports of frequent difficulty falling asleep were found to increase with age. Approximately 18% of the sample reported trouble waking in the morning, 11% indicated they woke in the night, 5% suffered from restless, disturbed sleep, and 3% woke up too early and were unable to return to sleep. They found no significant sex differences in any of the sleep disturbances reported . In general, poor sleep is associated with both behavioral and emotional problems. Occasional and chronic poor sleepers describe themselves negatively; they report being significantly more depressed moody, tense, irritable, lacking energy, and less rested and alert than good sleepers (KirmilGray et al., 1984). In a sample of 831 emotionally disturbed adolescents, Marks and Monroe (1976) found that sleep disturbances were associated with depression, anxiety and fear, and personality correlates, such as shyness, being quiet, slow, reserved, obsessive, anxious, fearful, phobic, having difficulty with concentration, and being sad and depressed. Price et al. (1978) also found that adolescent poor sleepers were worried, tense, less able to solve personal problems, and experienced low self-esteem, daytime fatigue, and mild depression. Tiredness has been found to be associated with measures of psychopathology (depression and anxiety), introversion, emotional instability, and cognitive anxiety (Montgomery, 1983). These findings reflect research in adult samples . For example, Ford and Kamerow (1989) found that adults who reported sleep disturbances were twice as likely to have a psychiatric disorder than those with no sleep disturbances. As part of a longitudinal study, Strauch and Meier (1988) administered a sleep questionnaire to students aged 10 to 14 years, with follow-up questionnaires administered five times at 2-year intervals. The authors concluded that a substantial proportion of the adolescents had difficulty adapting to the reduction in their sleep time that occurred in adolescence. The present paper derives from a longitudinal study that has investigated (among other things) the nature, prevalence J. Am. Acad. Child Adolesc. Psychiatry, 31: 1, January 1992

SLEEP PROBLEMS IN ADOLESCENCE

and persistence of emotional and behavioral disorders from childhood to adolescence. The aim of the present study was to document the prevalence of sleep problems at age IS in a large sample from the general population and to study the association between sleep problems and DSM-III disorder and social competence. The prevalence of sleep problems at age 13 and the persistence of these problems at age 15 was also examined.

Method Sample

The adolescents were enrolled in the Dunedin Multidisciplinary Health and Development Study, a longitudinal study of their development, health, and behavior. The study has assessed a large cohort born at Queen Mary Hospital, Dunedin, between April 1, 1972, and March 31, 1973. The first follow-up was conducted at age 3 when 1,037 of the 1,139 eligible children were assessed. Subsequent assessments have been performed at 2-year intervals, with 850 children being assessed at age 13 and 976 assessed at age 15. The characteristics of the study sample have been described in detail elsewhere (Silva, 1990). The sample is slightly advantaged in comparison with the rest of New Zealand on an index of socioeconomic status (Elley and Irving, 1972). It is also under-representative of Maori and Polynesian children in New Zealand. However, the sample would be comparable with other samples from Englishspeaking cultures. MEASURES

Mental Health Interview

Sample members were interviewed at age IS using a modified version of the Diagnostic Interview Schedule for Children (DISC-C, version Xlll- III) (Costello et aI., 1982). This structured interview schedule assessed disorders of childhood and adolescence, using DSM-III criteria. The adolescent self-report was used to identify the following disorders: 1) anxiety disorders, including social phobia, simple phobia, and overanxious and separation anxiety disorders; 2) depressive disorders, including dysthymia and current and past major depressive episodes; 3) attention deficit disorder, both with and without hyperactivity and also residual forms of the disorder; and 4) conduct and oppositional disorders. Identification of the disorder was based on the adolescent's self-report meeting the DSM-III criteria. The presence of criterion symptoms was only indicated by DISC-C questions eliciting a definite' 'yes" response. Full details of the assessment and procedure for identifying disorder are provided by McGee et aI., (1990). The DISC-C also provides symptom scores for these dimensions of disorder (Williams et aI., 1989). Scores on individual DISC-C items (0, 1, and 2 corresponding to "No," " Sometimes," and " Yes," respectively) were summed to produce symptom scores for anxiety (overanxiety, separation anxiety, and phobic disorder), depression (major depression and dysthymic disorder), attention deficit disorder-hyperactivity (ADD-H) (inattention, J.Am.Acad. Child Adolesc.Psychiatry,31:1, January1992

impulsivity, and hyperactivity), and conduct disorder (conduct and oppositional disorder). Included in the mental health interview were questions relating to the adolescents' sleep. They were asked if they had difficulty "falling asleep" ; "waking in the night and taking a long time to get back to sleep"; "waking up a long time before you have to"; "needing a lot more sleep than you used to" and "any other problems with your sleep, e.g., nightmares, sleepwalking?" (Sleep talking was not considered a problem, unless it disturbed the sample member or anyone else.) If the adolescents reported aproblem, they were asked "how long has that been happening?" Each response was scored as No = 0, Sometimes = 1, and Yes = 2. Yes responses required that the adolescent had experienced the sleep problem at least four times per week. Sometimes responses required the problem to occur from one to three times per week. Only responses scored with a 2, which had persisted for 4 weeks or more, were used in the analysis as indicating a sleep problem. Duration of the sleep problem was coded for a maximum of 12 months. Parent Questionnaire

The Revised Behavior Problem Checklist (RBPC) (Quay and Peterson, 1987) was completed by the parents of the sample. This is a 77-item questionnaire that assesses conduct disorder, socialized aggression, attention problem-maturity, motor excess, anxiety-withdrawal, and psychotic behavior. Social Competence

The social competence index comprised seven composite scores that came from the adolescents' own assessments of their school involvement, activities and leisure, work involvement, support and coping, strengths, and parent and peer attachment. The measure is fully described by McGee and Williams (1990). Six of the seven items making up the index were scored as 0, 1, and 2 representing low, medium, and high levels, respectively, of competence based on distributions of scores for each measure. Part-time work experience was scored as 0 or l. This resulted in a potential range of scores from 0 (indicating very low social competence) to 13 (very high social competence). Procedure

The sample members were assessed generally within 2 months of their 15th birthday, with the majority being seen at the Dunedin Unit, and a small proportion visited at home. Before commencing the interview, each adolescent was assured of the confidentiality of the information given. Written consent from both the adolescent and one of his or her parents was obtained before the interview.

Results Although 962 adolescents were interviewed with the DISC-C, complete sleep data were available for 943 adolescents at age 15 (484 boys and 459 girls). Prevalence of Sleep Problems

Overall, one-third of the sample (33.4%) had at least one sleep problem that occurred at least four times per week. 95

MORRISON ET AL. TABLE

1. Prevalence of Report ed Sleep Problems among 15-year-old Adolescents

Sleep Problem Falling asleep Staying asleep Early awakening Need more sleep Other sleep problems Two or more problems

Boys (%) (N = 484)

Girls (%) (N = 459)

Total (%) (N = 943)

9.1

10.0 3.0 4.4 25.9 2.8 8.3

9.6 2.2 3.4 25.3 2.5 7.3

1.5

2.5 24.8 2.3 6.4

Table 1 shows the proportions of boys and girls reporting sleep problems at age 15. There were no significant sex differences for any of the individual problems, and there was no significant sex difference in the numbers of boys and girls reporting multiple sleep problems. The most frequently occurring problem was needing more sleep; one in four adolescents reported needing more sleep than they used to. About 1 in 10 reported difficulty falling asleep; other problems were less frequent (less than 5%). Among the "other sleep problems," the most usual reports were of tiredness (38%), sleep talking (23%), sleepwalking (19%), and nightmares (12%). Other more unusual problems included falling out of bed a lot and waking with a sore throat after sleep talking. About 7% reported multiple (two or more) problems, most typically a combination of difficulty falling asleep and a need for more sleep. To investigate the relationship between sleep problems and symptom scores, the sample was divided into four groups: 1) those with no reported sleep problems (N = 628, 67%); 2) those indicating they needed more sleep only (N = 183, 20%); 3) a group comprising adolescents reporting difficulties falling asleep, maintaining sleep, or waking a long time before they had to (N = 52, 6%) (this group was collectively termed insomnia) ; and 4) adolescents reporting multiple sleep problems (N = 69,7%). Those 11 adolescents reporting "other sleep problems" in the absence of insomnia or need for more sleep were excluded from this analysis. These four groups were used in the subsequent analysis to examine the relationship between sleep problems and other DSM-III disorders, social competence, and behavioral problems. One-way analysis of variance (ANOVA) was used, followed by post-hoc Scheffe tests of significant results. Where ANOVA was inappropriate, chi-square tests were used. Self-report Symptoms Scores

To examine the relationship between sex, sleep problems, and symptom scores, a series of 2 X 4 ANOVAs were performed on the measures of anxiety, depression, inattention-hyperactivity, and conduct problems . None of the symptom scores showed significant sex X group interactions, so the results are reported for boys and girls combined. The results are shown in Table 2. There was a significant main effect for sleep problems for both anxiety and depression. Post-hoc Scheffe comparisons (with p < 0.05) indicated that those with no sleep problems were less anxious and had lower levels of depression than

96

those who needed more sleep, suffered from insomnia, and had multiple sleep problems. Those with multiple sleep problems reported significantly higher levels of anxiety and depression than those reporting insomnia or the need for more sleep. However, there were no significant differences in anxiety or depression between the latter two groups. A significant main effect was found for sleep problems on both the inattention and hyperactivity and conduct disorder scores. The post-hoc comparisons showed that those with no sleep problems had fewer reported inattention and hyperactivity problems and lower conduct disorder scores than those with sleep problems. However, there were no significant differences among the groups suffering from sleep problems. Parent Reported Behavior

The ANOVA revealed a significant main effect on the total RBPC score for sleep problems. The post-hoc comparisons indicated that those reporting insomnia or needing more sleep did not differ significantly from those with no sleep problems. However, those adolescents with multiple sleep problems had significantly higher parent-reported behavior problem scores. DSM-III Disorder

Table 3 shows the percentage of adolescents in each of the four groups identified as having a DSM-III disorder. Although the assessment of DSM-III disorder included a question pertaining to whether feeling depressed had affected their sleep, it was found that only two adolescents were included as depressed because of a positive response to this question. The majority of adolescents identified as depressed and having disturbed sleep according to DSM-III criteria had more than the required number of symptoms defining the disorder. The exclusion of these two adolescents did not significantly alter the results. Log-linear modelling (SAS, 1987) revealed no significant sex X sleep problem interaction, and so the male and female groups were combined in the subsequent analysis. Because of the small cell sizes, it was necessary to combine anxiety and depression (internalizing disorders) and also conduct and ADD-H (externalizing disorders) for the analysis. There were overall significant differences among the groups with X2 (3 df) = 64.54, p < 0.05, and post-hoc analyses using chi-square tests (Everitt, 1977) indicated significant differences (p < 0.05) between the three groups reporting sleep problems and those with no problems. Disorder was significantly more common in each sleep problem group than in the remainder of the sample. Of the 54 adolescents with multiple sleep problems or insomnia and with a DSM-III disorder, 36 (67%) had an anxiety or depressive disorder. In the group reporting a need for more sleep, 21 of the 50 with disorder (42%) had an anxiety or depressive disorder. For the remainder of the sample, disorders were equally divided between internalizing and externalizing types. Those with multiple sleep problems or insomnia were approximately three times more likely to have multiple DSM-III disorders or anxiety than those with no sleep problems (Table 3). J. Am. Acad. Child Ado/esc . Psychiatry, 31:1, January 1992

SLEEP PROBLEMS IN ADOLESCENCE

TABLE 2. Sleep Problems and Mental Health Measures at Age 15 Type of Sleep Problem (N = 69)

Insomnia (N = 52)

Need More (N = 183)

No Problems (N = 628)***

13.4 8.0 9.6 5.8 24.2

9.9 4.9 9.8 6.6 20.2

9.5 4.2 8.1 4.7 18.4

7.7 2.3 6.4 3.2 17.0

Multiple Mean Symptom Scores Anxiety Depression ADD-H Conduct Revised Behavior Problem Checklist

F(3,928)

23.89* 20.84* 19.23* 10.66* 4.87*

5.5 6.2 4.6 5.5 15.2

* All test statistics are significant at p < 0.05. ** y'MSE represents the square root of the mean square error term in the ANOVA and is an unbiased estimator of the standard deviation for the overall sample. *** Group cell sizes vary slightly across measures because of missing values.

TABLE 3. Sleep Problems, DSM-Ill Disorder, and Social Competence at Age 15 Type of Sleep Problem Type of Disorder Multiple disorder Anxiety Depression Conduct ADD-H None Poor social competence

Multiple (%) (N = 66)

Insomnia (%) (N = 51)

Need More (%) (N = 181)

11 21 4 12

8 22 2 10

2

o

4 8 3 10

50 33

58 25

73 17

Social Competence Measure Log lin ear modelling of so cial competence and sleep problems revealed no significant effect for the sex X group interaction, hence boys and girls were combined for subsequent analysis . There were overall differences among the sleep problem groups on the measure of social competence with X2 (3 d/) = 13.46, p < 0.05 (Table 3). Additional posthoc analyses examined differences among the sleep problem groups on social competence. A significant difference (p < 0.05) was found between the group reporting no sleep problems and those with multiple sleep problems who scored poorly on measures of social competence. Those adolescent s reporting insomnia or needing more sleep did not differ from the remainder of the sample on the measure of social competence.

No Problems (%) (N = 617) 3

6 I 5 I 84 17

2

dure. Of those with any kind of sleep problem at age 13, 48.5% had a sleep problem at 15. The results also indicated that there was a significant difference in the prevalence of sleep problems at the two ages with X2 (3d/) = 68.50, p < 0.01. The biggest differen ce was a two-fold increase from age 13 to 15 in the need for more sleep. Table 4 shows the percentage of each group at age 15 showing sleep problem s at 13. Log-linear analysis showed a small sex X group interaction with X2 (2d/) = 7.54 , p < 0.05, so the results are shown separately for boys and girls. Inspection of the table suggests that boys with multiple sleep problems and insomnia at 15, were more likely than girls reporting these problem s at 15 to have had a sleep problem at age 13. This was particularly the case for boys with insomnia at 15, three-quarters of whom reported sleep disturbance at 13.

Sleep Problems at Age 13 At age 13, sample members were asked identical questions about sleep problem s, and approximately one-quarter (22.6%) of the sample reported at least one sleep problem. The most frequentl y occurring problem s were difficulty falling asleep (11.6 %) and needing more sleep (11.8 %), whereas other problem s were less frequent (4.8% or less). Around 6% of the sample at age 13 reported multiple sleep problem s, with one-third of these adolescents reporting a combination of difficulty falling asleep and needing more sleep. Reports of sleep problem s at ages 13 and 15 were available for 704 adolescents. Changes occurring from age 13 to age 15 were analyzed using a log linear modelling proceJ. Am.A cad. Child Adolesc. Psychiatry, 31: I , January 1992

Discussion

The results of this study indicate that a relatively large proportion (33% of the sample) of adolescents experienced sleeping difficulties. The most often reported problems were a need for more sleep (25% of the sample) and difficulty falling asleep (10% of the sample). These findings support previous research indicating that a large number of adolescents experience sleeping difficulties (Bearpark and Michie , 1987; Kirmil-Gra y et al., 1984; Strauch and Meier, 1988). There were no significant differences between boys and girls in the number of sleep problems they reported. Similarly, there were no significant differences between boys and girls in the need for more sleep, insomnia, or multiple

97

MORRISON ET AL. T ABLE

4. Sleep Problems at Age 15 and History of Sleep Problems at 13 Sleep Problem at Age 15

Girls (N) History of sleep problem at 13 Boys (N) History of sleep problem at 13

Multiple

Insomnia

Need More

= 27) 44% (N = 25) 56%

(N = 21)

(N = 72)

19% (N = 15) 73%

26% (N = 77) 19%

(N

sleep problem groups. Finally, the absence of sex X sleep problem interactions across measures of anxiety, depression, ADD-H, conduct disorder, RBPC, DSM-III disorder, and social competence indicated that the association between sleep problems and psychopatholog y in adolescence is similar for boys and girls. Some studies (Kirmil-Gray et aI.,1984; Marks and Monroe, 1976; Price et al., 1978) have documented sex differences in reported sleeping problems, whereas others (e.g., Bearpark and Michie, 1987) have found no significant sex differences in any sleep disturbances. Adolescents reporting sleep problems were likely to report other problems, such as depression, anxiety, and other disorders. Those reporting no problems with their sleep had lower anxiety, depression , conduct disorder, and attention deficit disorder scores than those with sleep problems . Similarly, their parents reported fewer behavior problems ; they were less likely to have DSM-III disorder and poor social competence than those reporting problems with their sleep. Although the sleep problem groups con stituted appro ximately one-third of the sample, they represented one-half of those with a DSM-III disorder. (It should be noted that our modified DISC-C did not assess several other DSM-III disorders e.g., obsessive-compulsive and psychotic disorders.) The association between sleep problems and depression and anxiety confirms the earlier findings of Marks and Monroe (1976) and Kirmil-Gray et al. (1984). Multiple sleep problems were clearly associated with higher levels of psychopathology, and this was particularly so for anxiety and depression measures. Those with multiple sleep problems had significantly higher scores than those adolescents reporting needing more sleep or insomnia. They also had higher conduct and inattention scores than the remainder of the sample , but they did not differ from the other sleep problem groups. They were over three times more likely to have a DSM-III disorder compared with those with no sleep problems; twice as likely to have poor social competence; and their parents reported higher problem scores. Adolescents reporting insomnia or a need for more sleep also reported higher symptom scores than those with no problems. These findings suggest the importance of multiple sleep problems and insomnia as markers for mental health disorder. There was some suggestion that insomnia may be more strongly associated with DSM-III disorder and social competence than the need for more sleep. The prevalence of adolescent sleep problems increased over time from 25% of the sample at age 13 to 33% of the sample at 15. This change was predominantly in a need for more sleep at the later age, perhaps reflecting the stresses the adolescent faces. About half of those with sleep problems

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No Problems

= 219) 14% (N = 248) 22% (N

at 13 also reported problems at age 15. Furthermore, of those reporting multiple problems or insomnia at 15, nearly half reported a sleep problem at 13 indicating a relatively high level of chronicity associated with these kinds of sleep disturbance at 15. This was more so for boys. Early intervention, particularly in the case of multiple sleep disturbance and insomnia, may help avoid the development of these persistent sleep problems. Many adolescents in the present study reported experiencing sleeping difficulties and associated problems, such as anxiety, depression, and poor social competence. From the evidence presented here, it is not possible to identify whether sleeping difficulties play a causal role in adolescent emotional or behavioral problems . Ford and Kamerow (1989) maintained that sleep disorder may be an early sign or perhaps even the cause of some psychiatric disorders and suggest that early treatment may help in preventing the progression of the disorder. Other studies (Kirmil-Gray et al., 1984; Price et al., 1978) have emphasized the importance of good sleep habits, e.g., maintaining reg ular sleep tim es and avoiding other activities in the sleep environment. Given the relatively high proportion of adolescents with sleep problems and the degree of persistence of these problems over time, it would appear that good sleep habits are important skills for adolescents to learn. Finally, given the strong association between sleep problems and disorder in adolescence, the authors recommend the need for mental health professionals to take a careful sleep history in the evaluation of the adolescent patient. References Bearpark, H. M. & Michie, P. T., (1987), Prevalence of sleep/wake disturbances in Sydney adolescents. Sleep Res., 16:304. Costello, A., Edelbrock, C; Kalas, R., Kessler, M. & Klaric, S. A. ( 1982), Diagnostic Interview Schedule for Children (DISC). Contract No. RFP-D.3-81-0027. Bethesda, MD: National Institute of Mental Health. Elley, W. B. & Irving, J. C. (1972), A socio-economic index for New Zealand based on levels of education and income from the 1966 census. NiZ. J. Educ. Stud., 7:155-167. Everitt, B. S. (1977), The Analysis of Contingency Tables. London: Chapman & Hall. Ford, D. E. & Kamerow, D. B. (1989), Epidemiological study of sleep disturbances and psychiatric disorders: an opportunity for prevention? JAMA, 262:1479-1484. Kirmil-Gray, K., Eagleston, J. R., Gibson, E. & Thoresen, C. E. (1984), Sleep disturbance in adolescents: sleep quality. sleep habits, beliefs about sleep, and daytime functioning. J. Youth Adolesc., 13:375-384. Marks, P. A. & Monroe, L. J. (1976), Correlates of adolescent poor sleepers. J. Abnorm. Psycho/. 85:243-246. McGee, R., Feehan; M., Williams, S., Partridge, F., Silva, P. A. & J. Am. Acad. Child Adolesc. Psychiatry, 31: I, January 1992

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Kelly, J. (1990), DSM-III disorders in a large sample of adolescents. J. Am. Acad. Child Adolesc. Psychiatry. 29:611--619. - - Williams, S. (1991), Social competence in adolescence: preliminary findings from a longitudinal study of New Zealand 15-yearolds. Psychiatry 54:281-291. Montgomery, G. K. (1983), Uncommon tiredness among college undergraduates. J. Consult. Clin. Psychol. 51:517-525. National Board of Health and Welfare, Drug Information Committee (1988), Treatment of Sleep Disorders, Uppsala, Sweden, 4. Price, V. A., Coates, T. J., Thoresen, C. E. & Grinstead, O. A. (1978), Prevalence and correlates of poor sleep among adolescents. Am. J.

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Quay, H. C. & Peterson, D. R. (1987), Manualfor the Revised Behaviour Problem Checklist. Miami: Quay, H. C. & Peterson, D. R. SAS (1987), SAS/STAT Guide for Personal Computers, 6th edition. Cary, NC: SAS Institute, Inc. Silva, P. A. (1990), The Dunedin Multidisciplinary Health and Development Research Study. Paediatric and Perinatal Epidemiology. 4:96-127. Strauch, I. & Meier, B. (1988), Sleep need in adolescents: a longitudinal approach. Sleep. 11:378-386. Williams, S., McGee, R., Anderson, J. & Silva, P. A. (1989), The structure and correlates of self-reported symptoms in l l-year-old children. J. Abnorm. Child Psychol. 17:55-71.

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Sleep problems in adolescence.

A sample of 943 adolescents from the general population were questioned about sleep problems. A quarter of the sample reported needing a lot more slee...
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