The data were from Teen Health 2000 (TH2K), a community-based, prospective study of the epidemiology of psychiatric disorders among adolescents.[3
] The sample was selected from households in the Houston metropolitan area enrolled in local health maintenance organizations (HMOs). One youth, age 11–17 years, was sampled from each eligible household, oversampling for ethnic minority households. Every household with a child 11–17 years of age was eligible. Initial recruitment was by telephone contact with parents. A brief screener was administered to confirm ethnic status, age, and gender of youths. Because there were proportionately fewer minority subscriber households. Sample weights were developed and adjusted by poststratification to reflect the age, ethnic and gender distribution of the five-county Houston metropolitan area in 2000. The precision of estimates are thereby improved and sample selection bias reduced to the extent that it is related to demographic composition.[22
] Thus, the weighted estimates generalize to the population 11–17 years of age in a metropolitan area of 4.7 million people. Chi-square tests were used to compare ethnicity, gender and age distributions between census data for the five-county area and sample data. After the weighted procedure, no difference was identified between the two distributions with respect to the three demographic factors of age, gender, and ethnic group (p=0.99, p=0.93, p=0.99).
Data were collected at baseline on sample youths and one adult caregiver using computer-assisted personal interviews and self-administered questionnaires. Data collection was face-to-face, in the household or rarely, in another location specified by the family. The computerized interview contained a structured psychiatric interview (see below), demographic data on the youths and the household as well as queries about stress exposure. The interviews were conducted by trained, lay interviewers and took on average one-two hours, depending on the number of psychiatric problems present. The questionnaires contained questions on symptoms of sleep deprivation and insomnia and items assessing different risk and protective factors. These took about 30 minutes to complete. Interviews and questionnaires were completed with 4,175 youths (66% of the eligible households). There were no significant differences among ethnic groups in completion rates. Youths and caregivers were followed up approximately 12 months later using the same assessment battery used at baseline. The Wave 1 – Wave 2 cohort consisted of 3,134 youths plus their caregivers (75% of Wave 1 dyads). All youths and parents gave written informed consent prior to participation. All study forms and procedures were approved by the University of Texas Health Sciences Center Committee for Protection of Human Subjects.
There have been almost no studies of insomnia using DSM-IV diagnostic criteria for adolescents,[1
] and few thus far in the United States.[2
] None of the existing diagnostic interviews designed for epidemiologic research on psychiatric disorders originally included modules eliciting symptoms of sleep disorders. TH2K used the National Institute of Mental Health (NIMH) diagnostic Interview Schedule for Children, Version IV (DISC-IV).[23
To operationalize DSM-IV symptom criteria[24
] for a diagnosis of insomnia, the insomnia items are: difficulty initiating asleep (DIS), difficulty maintaining sleep (DMS 1 & 2, two items), early morning awakening (EMA), and non-restorative sleep (NRS). The time referent is the past four weeks. The DSM-IV symptom criteria for insomnia include all of these symptoms, and the symptoms should cause significant distress or impairment. To qualify for a diagnosis of primary insomnia, the symptoms must not occur exclusively during another sleep disorder, another psychiatric disorder or be due to the effects of alcohol, drugs or medication.
A number of risk factors and sequelae of sleep deprivation or insomnia among adolescents have been examined (for a review, see Roberts, Roberts and Chen[21
]). Covariates included here are age and gender of youths, family income, ethnic status, physical health functioning, mental health functioning and life stress. Age was treated as continuous variable as was family income. Ethnic contrasts at baseline are limited to European (n=1479), African (n=1476) and Mexican Americans (n=857). For these analyses the Wave 1 sample is 3812 rather than 4175 and the Wave 1-Wave 2 cohort is 2855. The smaller sample reflects the fact that there were not sufficient numbers of ethnic groups other than European, African or Mexican Americans to permit analyses.
Psychiatric disorders among youths were assessed with the DISC-IV, a highly structured instrument administered by lay interviewers. TH2K included anxiety disorders (agoraphobia, generalized anxiety, panic, social phobia, post-traumatic stress disorder), mood disorders (major depression, dysthymia, mania, hypomania), behavioral disorders (conduct, oppositional defiant, attention-deficit hyperactivity disorders), eating disorders (bulimia, anorexia nervosa), and substance use (alcohol, marijuana and other substance disorders). Three measures were constructed from the DISC-IV modules on mood disorders and substance use disorders. Because diagnostic criteria for depression include indicators of suicidal behaviors, disturbed mood was measured (whether youths had experienced depressed mood, anhedonia, or irritable mood) for a period of at least two weeks in the past year. Alcohol use was measured by reports of consuming any alcohol in the past year. Drug use similarly was assessed by use of marijuana and any other substances in the past year. The effects of substance use using a more stringent definition of 6 or more times in the past year also were examined. The results were essentially unchanged in terms of odds ratios. The less stringent definition increased effective sample size.
Outcomes examined are drawn from three conceptual domains representing somatic, psychological and interpersonal functioning and constitute major components of the lives of adolescents. See previous research by the authors.[21
] Psychological functioning was measured with two other indicators. One item asked youths to rate their life satisfaction as very satisfied, pretty satisfied, about equal, pretty dissatisfied and very dissatisfied. A second item asked youths to rate their emotional or mental health as excellent, good, fair, poor and very poor.
Interpersonal functioning was measured by three items that inquired the extent of problems (a lot, some, only a few, no problems) experienced with friends or peers, at home with family members, and at school. These measures have been used in previous research by the authors.[21
Somatic functioning, or physical health problems, was measured with three indicators. One item asked youths to rate how they perceived their health: excellent, very good, good, fair or poor. A second measure consisted of a scale asking how difficult in the past 4 weeks had physical health problems made it to perform 9 activities of daily living. Responses were not difficult, a little difficult, somewhat difficult, or very difficult. The score ranged from 0 to 27 (Cronbach’s α=0.88). A third measure assessed how often in the past 4 weeks health problems impacted 6 types of family activities. Responses were very often, fairly often, sometimes, almost never, and never. Scores ranged from 0–24 (Cronbach’s α=0.87).
Evidence cited earlier suggests school and work activities may impact sleep. Accordingly, the analyses included three items related to these domains. Each inquired whether during the past four weeks, the respondent slept less than usual (1) due to studying or homework, (2) because of school activities such as sports, clubs, etc., and (3) because of having a job. The percent still attending school in the initial wave was 97.8.
Covariates included in the current paper were age and gender of youths, ethnic status, family income, puberty status, and perceived body weight. Puberty status measured by asking youths to rate the growth of their body parts (height, body hair, breast, or voice). The score ranged from 0 to 9 (α=.75 for females and .74 for males).[26
] Youths were asked to describe their body weight with 5 categories: skinny, somewhat skinny, average weight, somewhat overweight, or overweight. This item was adapted from the Oregon Adolescent Depression Project.[27
] Although there is a literature on body weight and sleep disturbance (see[29
]), there also is evidence that body image and related attitudes may be more important than body weight per se in relation to psychosocial outcomes (see[30
]). For that reason, we included body image rather than body weight per se. Age, family income, puberty status, and perceived body weight were treated as continuous variables. Ethnic status was treated as categorical variable (European, African American, and Mexican Americans).
Analyses are presented defining insomnia several ways. First, data are presented on prevalence of any symptoms of insomnia. Youths with at least one of the insomnia symptoms without any exclusions were cases. This is termed P1. We then present prevalences of insomnia following DSM-IV criteria as closely as our data permitted. This is done in two ways. First, prevalence is estimated of at least one symptom of disturbed sleep with either daytime fatigue or daytime sleepiness (as indicators of impairment). This is termed P2. Second, that rate is then adjusted by excluding any subject who met the first two criteria who also met DSM-IV diagnostic criteria for a mood disorder, an anxiety disorder or a substance use disorder in the past year. This is termed P3. This is not equivalent to a full DSM-IV diagnosis of primary (or secondary) insomnia, but approximates such a diagnosis as measures permit.
Chronicity is defined as youths who met criteria for P1, P2 or P3 in Wave 1 and again in Wave 2. Here the focus is on the impact on functioning among youths who met criteria for P1, P2, or P3 in both Wave 1 and Wave 2. That is, they had to be a case in both waves.
For generation of confidence intervals for prevalence and odds ratio, survey mean (Proc surveymeans) and survey logistic regression (Proc surveylogistic) procedures in SAS V9.1[31
] were employed. This procedure uses Taylor series approximation to compute the standard error of the odds ratio. Lepowski and Bowles[32
] have indicated that the difference in computing standard error between this method and other repeated replication methods such as the jackknife is very small.
Definitions of functioning outcomes for analyses are as follows. Perceived health (self evaluated health status) has two categories: fair or poor (10%) and good and above (90%); Lower 50% of cumulative distribution of limitations and lower 50% of cumulative distribution of impact of illness were defined as low risk. Caseness groups for interpersonal problems were some/a lot problems (23%), a few/some/a lot problems (54%), some/a lot problems (27%) for home, peers and school respectively. In terms of psychological problems, satisfied and dissatisfied/pretty dissatisfied/very dissatisfied were categorized as lower life satisfaction; any one who had at least one of three depression symptoms was defined as depressed mood; overall emotion or mental health of fair or below fair were in the high risk group. Alcohol use/other drug use were set to anyone who used alcohol/other drugs in the past 12 months. Sleep less due to activities have 3 categories: sleep less often/almost everyday due to school work/school activities in the past 4 weeks was the high risk; sleep less sometimes/often/almost everyday due to having a job was the high risk group.