Methodology Considerations
As one of the few studies
(1,
8,
28) that have investigated the prevalence and the time trend for adolescent psychiatric morbidities, the present study provided a unique opportunity to compare the sex and the urban-rural difference of such morbidities between developing and developed countries. Our study has employed the two-stage design, and all the clinical interviews were conducted by child mental health professionals with the standardized Chinese K-SADS-E with cross-cultural validation and acceptable interrater reliability. Consensus psychiatric diagnoses were made through independent assessment of the Chinese K-SADS-E interview records and a joint discussion by two senior research psychiatrists. The response rates at phase I and the two follow-ups were very high.
Despite all of these strengths, there are some limitations of this study that require careful consideration in the interpretation of the findings. First, because of a purposeful sampling of study schools, its external validity for other Taiwanese adolescent populations needs to be examined. Second, the psychiatric diagnoses were mainly based on clinical interviews of study subjects without interviewing their parents. Previous studies have shown low agreement among child, parent, and teacher informants in reporting children’s emotional and behavioral problems
(29) and the need to incorporate teachers’ reports into the identification of externalizing disorders
(29). Therefore, we included the teacher report form to make the best estimates of psychiatric diagnoses of ADHD, conduct disorder, and oppositional defiant disorder. Finally, in this two-stage case-finding study, despite the fact that all the study subjects were screened at the first stage for 3 consecutive years, the second-stage psychiatric interview was not performed among all of them. The lack of complete information in psychiatric diagnoses for all study subjects has prevented us from conducting longitudinal analyses using a multilevel model to examine the trajectories of psychiatric diagnoses at an individual level.
Prevalence and Trend
The magnitude of total psychiatric morbidities estimated in this study was in the middle of previous studies
(5,
6) and was similar to those (20.9% and 20.3%) of two large-scale epidemiology studies of youths in the United States
(4,
8). However, the clinical interview and diagnostic criteria (DSM-III-R) used in those two U.S. studies were different from those in this study. Shaffer et al.
(4) employed the National Institute of Mental Health’s Diagnostic Interview Schedule for Children, Version 2.3, and Costello et al.
(7) used the Child and Adolescent Psychiatric Assessment.
Although there was only a minor change in the diagnostic criteria for ADHD from DSM-III-R to DSM-IV, the average estimated prevalence of ADHD has been reported to increase from 3%–5% with DSM-III-R to 9%–10% with DSM-IV with the three newly created subtypes
(11,
30). The overall prevalence of ADHD in this study was close to the figures in recent studies in Australia
(31) with the Diagnostic Interview Schedule for Children and in Brazil
(32) with the 18 DSM-IV ADHD symptom items and clinical diagnosis. Similar to findings in previous studies
(15), the rates of ADHD declined over adolescence. Our rates of conduct disorder and oppositional defiant disorder were in the lower part of the reported rates across cultures and countries
(8,
33), with a nonsignificant increase for conduct disorder over the 3 years in boys.
A unique finding of this study is that unlike Western societies
(19), betel instead of alcohol was the second (after nicotine) most prevalent abused substance among our study subjects, which might be attributable to an increased availability of betel because of commercial interest in recent years and the popularity of the betel chewing habit, particularly in rural areas
(9). The fact that all the study subjects with substance use disorders had nicotine use disorder and the rates of nicotine dependence had markedly increased over time strongly indicates the seriousness of nicotine damage on health among Taiwanese adolescents today.
The 3-month prevalence rate of depressive disorders in this study was somewhat lower than those in previous studies, which largely reported 6- or 12-month prevalence rates in similar age populations
(4,
8). However, our finding of a significant increase in time trend of such morbidity in both sexes was consistent with previous work
(20).
Consistent with previous studies, specific phobia was the most common anxiety disorder, followed by social phobia, then generalized anxiety disorder
(12–
14). The lower trend in the rates of total anxiety disorders mainly came from specific phobia, social phobia, and separation anxiety disorder
(16), and girls had a greater stability of internalized disorders than boys over time
(34).
Urban-Rural Difference
Our findings of higher rates of conduct disorder/oppositional defiant disorder and substance use disorders in rural areas, although contrary to that in earlier Western studies
(18,
33), were in accordance with those from recent studies in Western
(37) and Asian societies
(9). The finding of a greater increase in time trend for substance use disorders in rural areas in this study awaits further examination in other societies.
Urban-rural differences in psychiatric morbidity are likely to be associated with multiple social environmental factors. Urban neighborhood as a risk factor for psychiatric disorders has been explained by its close association with lower socioeconomic status in most cities in developed countries
(38). This notion might have at least in part explained the higher rates of conduct disorder/oppositional defiant disorder, substance use disorders, and total psychiatric morbidities among adolescents in rural Taiwan, where the socioeconomic status has been generally lower than in their urban counterparts
(9,
39). Another important factor for such difference in morbidity in Taiwan may have come from a positive selective migration of the mentally fit from rural to urban cities
(39). For example, rural children from the families of higher socioeconomic status move to urban cities for better educational opportunities, leaving behind those who are more socioeconomically disadvantaged and less academically competent, with a higher vulnerability to both psychological disorders and substance abuse
(9). In consequence, performance on the Joint Entrance Examination for Senior High School is generally better among urban junior high schools than among their rural counterparts
(9).
Findings regarding the relationships between low socioeconomic status and anxiety and mood disorders have been contradictory
(8,
35). The present study did not find any significant association between urban or rural residency, a proxy for socioeconomic status, and the rates of ADHD, depressive disorders, and most anxiety disorders. Our finding of different time trends for specific phobia and social phobia across urban or rural residency may deserve further inquiry. It is likely that environmental exposure may last longer for specific phobia in rural areas globally and may be higher regarding the pressure from social contact and school performance in urban areas in developing countries.
Implications for Prevention
It is imperious to provide a protective environment to prevent childhood-onset emotional and behavioral disorders and substance-related disorders among vulnerable adolescents. Our findings have implied that the amelioration of detrimental risk factors in social environment (be it more prevalent in rural or urban settings in different societies) for mental disorders in adolescents may serve as the target for primary prevention. Betel abuse, a specific disorder in Taiwan and certain Asian countries, ought to be prevented among both adolescent and adult populations, especially in rural areas. Further investigation of risk factors, patterns of comorbidity, and the trajectories of psychopathology during adolescence is crucial for the identification of the target for primary prevention among different vulnerable groups.