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Prevalence and Comorbidity of Child and Adolescent Disorders in Western Australian Mainstream School Students.

Shane Langsford PhD

Stephen Houghton PhD

Graham Douglas PhD &

Ken Whiting MD

Centre for Attention & Related Disorders
The Graduate School of Education
The University of Western Australia

Address for Correspondence:

Prof Stephen Houghton
Centre for Attention & Related Disorders
The University of Western Australia
Nedlands, Perth 6009
Western Australia

Email Author

Abstract

The purpose of the present research was to determine the prevalence and patterns of comorbidity of disorders among Western Australian mainstream primary school and secondary school aged students. Seven hundred and four children and adolescents from four primary (Years 5 and 7) and six secondary schools (Years 9 and 11) in the Perth metropolitan area of Western Australia, participated in the study. The Australian Child and Adolescent Screening Inventory (ACASI: Langsford, 1999) which consists of 136 items covering 21 disorders was administered under standardised conditions. Results revealed that 48% of participants self-reported at least one disorder. The proportion of males reporting a disorder was greater than that of females. Dysthymic disorder was found to be the most prevalent disorder, followed by tic disorders, oppositional defiant disorder, and conduct disorder. Approximately 54% of participants self-reported two or more disorders, with mixed receptive-expressive learning disorder being the most comorbid. Significant differences were found according to Gender, Age, and Socioeconomic status. Comorbidity must be considered in the design of research on disorders in children and adolescents.

Introduction

Although there are published studies that have examined the prevalence of disorders in clinic samples, there appears to be very few studies which have investigated the prevalence of disorder(s), (i.e., collective disorder and individual disorders) in mainstream school children and adolescents. Given that relatively recent studies (e.g., Kessler et al., 1994; Fergusson et al., 1993) have suggested that a significant number (>20%) of children and adolescents in the mainstream population present with at least one disorder, this is an important area to address. Studies have also reported comorbidity (i.e., the occurrence at one point in time of two or more disorders, Clarkin & Kendall, 1992) from as low as 25% (McGee et al., 1990) to as high as 68% (Offord et al., 1987).
Early surveys of the prevalence of disorder reported rates of 17.5% (Lagner et al., 1974); 21.0% (Graham & Rutter, 1973); 25.4% (Rutter, Cox, Tupling, Berger, & Yale, 1975); and 26.0% (Verhulst, Berden, & Sanders-Woudstra, 1985). However, many of these earlier studies were characterised by inconsistencies (e.g., child and adolescent samples obtained exclusively from medical centres, employment of questionnaires which were not validated against clinical judgement, differing types and definition of disorder, and different diagnostic systems utilised, masking effect of comorbidity not addressed); therefore data need to be interpreted with a degree of caution.
Of the more recent research, the Ontario Child Health Study (OCHS: Offord et al., 1987) which was conducted in Canada with 2674 children and adolescents aged between 4 and 16 years, reported an overall six-month prevalence rate for conduct disorder (CD), hyperactivity, emotional disorder (anxiety and depression), and somatisisation (sickliness without cause) of 18.1%. The prevalence rate in children aged 4 to 11 years was higher among males than females (19.5% vs 13.5%), while the reverse was true among adolescents aged 12 to 16 years (18.8% males and 21.8% females). Adolescent males were also found to have a higher prevalence of CD (8.1% vs 2.7%) and hyperactivity (8.9% vs 3.3%) than females, with the older age group (12-16 years) reporting significantly higher prevalence than the younger age group (4-11 years). Comorbidity was found to be high, with 68% of the sample having one or more additional disorders (Offord et al., 1987).
The Puerto Rico Child Psychiatry Epidemiologic Study, (PRCPES: Bird et al., 1988) reported a similar six-month prevalence rate of 17.9% for 6 to 16 year-olds. Rates of disorders across three age groups in this sample (4-5 year-olds, 6-11 year-olds, and 12-16 year-olds) indicated that the prevalence rate of ADHD was lowest in the youngest age group (4-5 year-olds), compared to the two older groups. Also the rate of depression was higher in each successively older group, while separation anxiety disorder (SAD) was found at a higher rate in the 6 to 11 year-old group than in both the younger and older groups. Comorbidity among disorders was found in 46.1% of the sample.
The National Institute of Mental Health (NIMH) Primary Care Pediatric Study (PCPS: Costello, 1989b) initially found a prevalence rate of 24.7% for one or more DSM-III disorders among 789, 7 to 11 year-olds in Pittsburgh, USA. Detailed follow-up interviews, yielded a prevalence rate for one or more DSM-III disorders of 22.0% + 3.4%.

Two separate studies, the New York Child Longitudinal Study, (NYCLS: Velez et al., 1989) and the Dunedin (New Zealand) Multidisciplinary Health and Development Study (DMHDS: McGee et al., 1990) reported prevalence rates for disorder of 17.7% (9-18 year-olds) and 22% (15 year-olds), respectively. In the DMHDS (McGee et al., 1990), prevalence rates of disorder were reported as 25.9% for females and 18.2% for males, with the overall female predominance for disorder being attributed to higher prevalence of anxiety disorders (AnxDs) and depressive disorders (DepDs). Data also revealed a male-female ratio for diagnosis in 11 year-olds of 1.3:1. Males exhibited more ADHD, CD, oppositional defiant disorder (ODD), and depression, while girls more commonly exhibited AnxDs. Comorbidity was reported to be as high as 68% (McGee et al., 1992). When the prevalence rate for the majority of the 11 year-olds was adjusted for comparability with the data for follow-up four years later (at 15 years of age), the overall prevalence rate rose from 17.6% to 19.6%. Four years later (at 15 years of age) the male-female ratio had shifted to 0.7:1, with higher rates for girls for all disorders except ADHD (McGee et al., 1992).
One of the few studies not to have produced elevated prevalence rates in the older age groups was undertaken in Germany by Esser et al. (1990). Parent and teacher reports of 8 year-olds revealed a six-month disorder prevalence rate of 16.2%. At age 13 years, prevalence rates were remarkably similar: 16.2% without adolescent interview data, and 17.8% with adolescent interview data. The effect of age on prevalence and incidence of disorder was found to be not significant.
One of the few longitudinal studies (and the first to use DSM-III-R diagnoses) was the Christchurch Health and Development Survey (CHDS: Fergusson et al., 1993) in New Zealand. Overall, approximately 25% of children met the criteria for at least one DSM-III-R diagnosis. Prevalence rates of disorder were higher for girls (32.55%) than for boys (20.35%), with the difference being largely attributed to higher rates of AnxDs and mood disorders among girls. Fergusson et al., (1993) reported that 41% of children met criteria for at least two diagnoses, with more than 10% meeting criteria for three or more diagnoses.
Kashani et al. (1989) also found higher rates for AnxDs among girls: 28.6% of 7 to 17 year-old females reported GAD in comparison with 13.3% of boys. ODD rates in 14 to 16 year-old adolescents was also found to be higher for girls (8%) than boys (4%).
The most recent survey comprising prevalence data is the Western Australian Child Health Survey (WACHS: Garton, Zubrik, & Silburn, 1998) which reported that "mental health morbidity" was identified in 17.7% of the sample, with 12 to 16 year-olds displaying a higher morbidity than 4 to 11 year-olds (21% versus 16%). In addition, more 4 to 16 year-old males (20%) presented with a disorder than females (15.4%). Garton et al., (1998) reported that 32.2% of individuals presented with one disorder, while 67.8% indicated two or more. However, findings from this study need to be interpreted with a degree of caution since the survey instrument "probes behaviours indicative of mental health morbidity" (Garton et al., 1998, p. 35). Furthermore, categories of disorder, namely delinquent behaviour, aggressive behaviour, withdrawn, anxious/depressed, somatic complaints, social problems, thought problems, and attention problems are not commensurate with the widely used diagnostic categories for disorders (i.e., DSM).
Prevalence rates reported for individual disorders are characterised by greater variance. For example, the prevalence of GAD has been reported from as low as 1.6% (Wittchen, Zhao, Kessler, & Eaves, 1994) to as high as 21% (Kashani, Orvaschel, Rosenberg, & Reid, 1989). It is not possible to report the full range of disorder prevalence rates in this article, therefore in the interest of brevity, the range of prevalence findings for the most common child and adolescent disorders are provided in Table 1. These reported prevalence data reflect those individuals who have been identiffied and subsequently referred for diagnosis and treatment.
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Insert Table 1 here
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While the studies cited in Table 1 represent recent and, to date, accurate estimates of the prevalence of disorder, they are not entirely satisfactory. For example, the majority of these studies tend to reflect only those individuals who have been identified and subsequently referred for diagnosis and treatment. The majority of children and adolescents with a disorder are not identified (Anderson et al., 1987; Costello, 1989b; Costello et al., 1988; Offord et al., 1987) and hence the prevalence rates in these studies are under-reported.
The studies which have addressed socioeconomic status (SES) have suggested a greater prevalence of disorder among lower SES groups (Bruce et al., 1991; Holzer et al., 1986; Tongue, 1998; Weich et al., 1997; Williams et al., 1992). Almost all of these, however, are based solely on adult studies, with few articulating the developmental course of disorder(s). Evidence suggests an association between early onset of a disorder and greater comorbidity with other disorders (Kasch & Klein, 1996). Therefore, describing a disorder's developmental course is important. Finally comorbidity has not been adequately addressed in studies to date.
This research will attempt to address these issues by investigating prevalence of disorders and patterns of comorbidity in mainstream primary and secondary school children and adolescents in Perth, Western Australia. Where applicable, prevalence patterns according to Age, Gender, and SES will be investigated.

Method

Participants

The sample comprised 704 children and adolescents (313 males and 391 females) aged 10 to 18 years of age, from each of Years 5 (age 10-12 years, n=76) and 7 (age 12-13 years, n=85) from four primary schools, and from Years 9 (13-15 years, n=341) and 11 (16-18 years, n=202) from six secondary schools. These schools were designated a SES (i.e., low, medium, and high) according to Australian Bureau of Statistics (ABS: Broom, Duncan-Jones, Lancaster-Jones, McDonnell, 1977) demographic location.

Settings

Ten schools (four primary and six secondary) participated in the research. Of the primary schools one was classified as low to middle SES, one middle SES, one middle to high SES, and one high SES. Two of the high schools were classified low SES, one was low to middle SES, two were middle SES, and one was high SES. The number of students enrolled at the primary schools ranged from 195 to 530, and at the high schools from 800 to 1240.
All participants completed the Australian Child and Adolescent Screening Inventory (ACASI, Langsford, 1999) uninterrupted in the regular classroom of their respective school. A test environment was established to reduce the amount of noise and interaction between students. Students not involved in the study were instructed by their teacher that they were permitted to silent read or begin their homework while the others completed the instrument.

Instrumentation

The Australian Child and Adolescent Screening Inventory (ACASI: Langsford, 1999).
The ACASI (Langsford, 1999), which was adapted from the Adolescent Screening Inventory - 4 (Gadow & Sprafkin, 1997), is designed for use with children and adolescents aged between 10 and 17 years. It consists of three separate, yet commensurate, screening forms (a Self-report Form, a Parent-report Form, and a Teacher-report Form). In the present investigation only the Self-report Form was administered. This form contains 136 randomly allocated items based on diagnostic criteria provided in the DSM-IV, to which participants respond on a four-point ordered scale, described by the words Never, Sometimes, Often, or Very Often. Seven items within the ACASI are slightly reworded, and repeated in random positions, to provide a measure of rater reliability.
The 136 items cover 21 disorders as follows: generalised anxiety disorder (GAD), obsessive-compulsive disorder (OCD), posttraumatic stress disorder (PTSD), separation anxiety disorder (SAD), attention-deficit/hyperactivity disorder (ADHD), conduct disorder (CD), oppositional defiant disorder (ODD), bipolar disorder (BD), dysthymic disorder (DD), anorexia nervosa (AN), bulimia nervosa (BN), tic disorder (TicD), tourette's disorder (TD), asperger's disorder (AsD), autistic disorder (AD), expressive language disorder (ELD), mixed receptive-expressive learning disorder (MRE), phonological disorder (PD), disorder of written expression (DWE), mathematics disorder (MD), and reading disorder (RD). The three ADHD subtypes (inattentive, hyperactive-impulsive, and combined) and two TicD subtypes (motor and vocal) are also included.
The inclusion of these disorders in the ACASI was based on previous research (Langsford, 1998) which utilised a questionnaire survey to identify disorders for which Western Australian educational psychologists (n = 72) had received referrals during the 1998 school year. As an additional check, school teachers (n = 7) and clinical psychologists (n = 8) were contacted and asked what disorders they came into contact with in their classrooms/practice. The clinical psychologists were also asked if there were any disorders other than those cited by the educational psychologists, for which had they received referrals. None of the clinical psychologists volunteered any additional disorders.
Research conducted with a sample of 823 students aged 10 to 18 years (385 males and 438 females) has demonstrated that the ACASI is a valid and reliable instrument (Langsford, 1999). Statistics of agreement for a positive screen among students, parents, and teachers ranged from .77 to .93, and calibration with a clinically diagnosed sample revealed over 80% agreement. The ACASI also has a Flesch-Kincaid readability grade level of 4.9 which indicates that it is suitable for children in Years 5 onwards (i.e., 10 years of age and above).

Scoring of the ACASI

Participants are required to shade the circle that best represents the frequency of their behaviours (i.e., Never, Sometimes, Often, or Very Often). Scoring of the items (for all three Forms of the ACASI) is based on the frequency of the child or adolescent's behaviour. When calculating disorder screening scores the items for all categories, with one exception, are scored as: Never = 0, Sometimes = 0, Often = 1, and Very Often = 1. These values were chosen because although many people with and without disorders may exhibit similar behaviours, it is the frequency of the behaviour that is important. The one exception is for CD where seven of the behaviours (e.g., fighting with a weapon, stealing) are considered to be so severe that 'Sometimes' is also awarded a score of 1 (Gadow & Sprafkin, 1997; Lagenbucher, Morgenstern, Labouvie, Miller, & Nathan, 1996). Therefore, the summation of the items within each disorder produces a criterion score for that disorder, which if exceeding the screening cutoff score (i.e., as stipulated by DSM-IV), designates the individual as a positive screen for that disorder.
It should be noted that a positive screen is not a diagnosis, rather it indicates that the individual has met sufficient criteria for a disorder to warrant further investigation by an appropriate professional.

Procedure

Consent to participate was initially obtained from the principals of the ten schools. The schools were selected on the basis of their SES. An information sheet and parental consent form was subsequently posted to the parents of all children in each of Years 5, 7, 9, and 11 from each of the schools. It was stressed to parents that all data collected were confidential, and that no information would be made available to other sources without parental permission. All children who returned their consent form were included in the research. A 90% return response rate was achieved.
Written instructions were provided for participant's regular classroom teachers who distributed the ACASI during a class period. This ensured standardisation in test administration. On completion of the ACASI, students placed their questionnaires in an envelope which they then sealed to ensure confidentiality. The first author subsequently collected all completed questionnaires.
In order to test for the agreement of the responses of the individual participants, the responses to the seven repeated items were extracted and matched with their corresponding repeat. The rater reliability between the seven repeated items was examined using a modified version of the C ordinal statistic (Cicchettii, 1972) which applied weights reflecting the level of agreement/disagreement between two items on rank ordered scales.

Results

Overall prevalence

Of the 704 participants who completed the ACASI, and who exhibited sufficient rater-reliability for inclusion, 48.01% (n = 338) self-reported at least one positive screen. The proportion of males reporting a positive screen was greater than that of females (156/313=49.84% males; 182/391=46.55% females), but this was not statistically significant. As can be seen in Table 2, the most prevalent disorder was DD, followed by TicD, ODD, and CD. None of the other disorders reached 10% prevalence. There were a number of significant Gender differences in relation to individual positive screens. Significantly more males than females self-reported a positive screen for CD, DWE, and RD. Conversely, significantly more females self-reported a positive screen for DD and AN.
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Table 2 here
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When the data were collapsed to form two disparate Age groups (Primary and Secondary school) the relative percentages indicated that a greater number of secondary aged students (269/543=49.54%) self-reported a positive screen, than did primary aged students (69/161=42.86%). Secondary school participants self-reported a significantly greater proportion of positive screens for all of the ADDBD (ADHD, CD, and ODD) as well as DD. No instances were found where the primary school group reported a significantly greater proportion for any of the positive screens.
SES was significant (X2 p = .008) in relation to positive screen, and this was mainly attributable to the High SES group self-reporting very few positive screens in comparison to the other groups: High SES (22/71=30.99%), Medium SES (190/372=51.07%), and Low SES (126/261=48.28%). SES was also significant for individual positive screens (ADHD, CD, ODD, and RD) and this was attributable to the High SES group self-reporting very few positive screens.

Comorbidity

To determine the extent of comorbidity the Positive Screen group (i.e., all those who self-reported at least one disorder) was categorised according to the total number of positive screens self-reported by each individual. The total number of positive screens, and hence, the extent of comorbidity, is shown in Table 3.
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Table 3 about here
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As can be seen in Table 3, 156 (46.15%) of the 338 participants self-reported a single positive screen. In comparison, 182 (53.85%) self-reported two or more positive screens, the difference in proportions between these two groups not being statistically significant.
Table 4 shows the percentages of comorbidity among each of the 21 disorders. These percentages were averaged and then rank ordered to examine the extent of comorbidity in each of the disorders. (Bipolar Disorder, Asperger's Disorder, and Autistic Disorder were removed because of their small cell sizes, i.e., below 10). Table 4 demonstrates that MRE was most comorbid, followed by DD, ODD, ADHD, and CD. The two eating disorders, BN and AN demonstrated the lowest levels of comorbidity.
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Table 4 about here
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Discussion

This research sought to determine the prevalence of child and adolescent disorders in mainstream primary and secondary school populations. In doing so the research attempted to address the methodological problems which have characterised some of the earlier research (e.g., extrapolation of prevalence rates from clinic samples, unreliability of diagnostic instrumentation used, various definitions of disorder, and different diagnostic systems utilised). To do this the ACASI (Langsford, 1999), which is a reliable and valid instrument calibrated against a clinically diagnosed population, was utilised.
Results revealed that 48.01% of mainstream children self-reported a positive screen for at least one of the disorders. This is highly comparable with the most recent study (NCS: Kessler et al., 1994) which reported prevalence of at least one disorder as 48%. Although most of the other studies cited produced considerably lower prevalence rates, many were based on the investigation of only a small number (3 or 4) of disorders, and used earlier diagnostic systems (i.e., earlier DSMs versus the current DSM-IV). Consequently there has been variation in reported rates. The present study, however, utilised DSM-IV criteria for 21 disorders, and therefore prevalence rates (both collective and individual) may be more representative of the true prevalence rate.
Tic disorders and ADDBDs were among those most frequently self-reported and given the overt nature of these, individuals would more easily recognise the symptoms. However, the most prevalent was DD which is an internalising disorder. While this may not be so easily (overtly) identifiable to others, the individuals in the present study were able to match their symptoms to the DSM-IV criteria and subsequently self-report its occurrence. In recent research, Western Australian clinical psychologists have reported that their most frequent referrals pertaining to adolescence are for DepDs (Langsford, 1999).
As reported in the literature (e.g., Kandel & Davies, 1986; Kashani et al., 1987; Lewinsohn et al., 1993; McGee et al., 1990; Nottelmann & Jensen, 1995), females in this study self-reported DD and AN more frequently than males, whereas males self-reported significantly more positive screens for CD, DWE, and RD. In addition, secondary school participants self-reported significantly more positive screens for all of the ADDBD (ADHD, CD, and ODD) as well as DD which is in line with the findings of Bird et al. (1988), Garton et al. (1998), and Nottelmann and Jensen, (1995). That prevalence rates of the majority of disorders steadily increase from late childhood through mid-to-late adolescence has been previously documented (e.g., Garfinkel & Garner, 1982; Newman et al., 1996; Rapoport, 1986; Rutter et al., 1976).
A greater proportion of disorder was self-reported in lower SES areas which again is in agreement with the majority of the literature (e.g., Bruce et al., 1991; Holzer et al., 1986; Tongue, 1998; Weich et al., 1997; Williams et al., 1992).
With reference to comorbidity, the findings of this study indicated that of the participants self-reporting a positive screen, 54% self-reported more than one positive screen. Thus, comorbidity was found to be extensive. Indeed, studies (e.g., Kessler et al., 1994) have found that comorbidity is the rule rather than the exception. It may be therefore, that a dimensional approach to classification might be more parsimonious than a categorical approach (Blashfield, 1990; Brown & Barlow, 1992).
Of the individual disorders, MRE was the most comorbid. This is in agreement with Ruhl, Hughes, and Camarata (1997) who found a greater probability for children and adolescents with communication disorders to have concomitant emotional/behavioural difficulties; those with psychiatric problems also tended to have communication problems.
In line with the prevalence data, DepDs and the ADDBD were most prevalent. Attention-Deficit and Disruptive Behaviour Disorders are overt and readily identifiable, however, in this study it was children's self-report data that identified them as highly prevalent. The data from this present research is very similar to that provided by Western Australian school psychologists who cited DepDs, ADDBD, and LD as those most frequently referred to them (Langsford, 1999).
It is clear, therefore, that comorbidity must be considered in the design of research on disorders in children and adolescents. Kendall and Clarkin (1992) called for continued studies of the frequency of comorbidity and related conditions, examination of symptom overlap and the potential role of symptoms in defining boundaries between related disorders, as well as to studies of differential effects of treatment of children with comorbid disorders and of children who, within the same disorder, differ on etiological factors (Nottelmann & Jensen, 1995).
That Age and Gender differences were identified suggests that further research is necessary so that more appropriate and effective instructional strategies for females as distinct from those used with males might be developed.
In conclusion, the present research has provided important data pertaining to the prevalence and patterns of comorbidity of disorders in mainstream child and adolescent populations. Moreover, this was achieved using a new and valid screening instrument based on DSM-IV diagnostic criteria.

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Table 1
Range of prevalence data for the most common disorders according to the literature

Disorder Category Lowest Highest
Specific Disorders %/Age/Author(s) %/Age/Author(s)

Anxiety Disorders
Generalised Anxiety Disorder 1.6/15-54/Wittchen et al., 1994 21.0/8-17/Kashani et al., 1989
Obsessive-Compulsive Disorder 1.0/14-18/Flament et al., 1994 7.1/21/Newman et al., 1996

Attention-Deficit and Disruptive Behaviour Disorders
Attention-Deficit/Hyperactivity Disorder 1.2/15/McGee et al., 1992 12.6/9-18/Velez et al., 1989
Conduct Disorder 2.0/11/McGee et al., 1992 11.7/9-18/Velez et al., 1989
Oppositional Defiant Disorder 1.3/11/McGee et al., 1992 18.6/13-18/Velez et al., 1989

Communication Disorders
Expressive Language Disorder 2.69/0-17/Dyrborg & Goldschmidt, 1996 15.2/1-6/Baltaxe & Simmons, 1988a
Mixed Receptive-Expressive Language Disorder 2.61/0-17/Dyrborg & Goldschmidt, 1996 9.6/1-6/Baltaxe & Simmons, 1988a
Phonological Disorder 0.5/17/APA, 1994 2-3/6-7/APA, 1994

Depressive Disorders
Dysthymic Disorder 1.4/11/McGee et al., 1992 6.4/8-11/Polaino-Lorente & Domenech, 1993

(Table 1 continued over page)

(Table 1 continued)

Disorder Category Lowest Highest
Specific Disorders %/Age/Author(s) %/Age/Author(s)

Eating Disorders
Anorexia Nervosa 0.3/13-18/Whitaker et al., 1990 0.40/15/Rastam, Gillberg, & Garton, 1989
Bulimia Nervosa 0.02/10-64/Hoek et al., 1995 0.63/15-65/Garfinkel et al., 1995

Learning Disorders
Disorder of Written Expression * *
Mathematics Disorder 1.3/9-10/Lewis, Hitch, & Walker, 1994 6.5/11/Gross-Tsur, Manor, & Shalev, 1996
Reading Disorder 2/6-17/Riccio & Hynd, 1995 8/7-10/Shaywitz, Shaywitz, Fletcher, & Escobar, 1990

Pervasive Developmental Disorders
Asperger's Disorder 0.36/7-16/Ehlers & Gillberg, 1993 .71/7-16/Ehlers & Gillberg, 1993
Autistic Disorder 0.08/2-4/Baron-Cohen et al., 1996 .12/4-13/Gillberg, Steffenburg, & Schaumann, 1991

Tic Disorders
Tic Disorder (Motor & Vocal) 3/10-14/Kurlan et al., 1994 10/6-12/Fallon, Jr. & Schwab-Stone, 1992
Tourette's Disorder 0.03/5-18/Caine et al., 1988 2.99/13-14/Mason et al., 1998

* No prevalence rates available as at August 1999

Table 2
Australian Child and Adolescent Screening Inventory prevalence for the 21 disorders (n=704)

Disorder Category Total Male Female p
Specific Disorders % N N

Anxiety Disorders
Generalised Anxiety Disorder 6.39 17 28
Obsessive-Compulsive Disorder 4.69 10 23
Posttraumatic Stress Disorder 5.97 12 30
Separation Anxiety Disorder 5.54 15 24

Attention-Deficit and
Disruptive Behaviour Disorders
Attention-Deficit/Hyperactivity Disorder 7.39 28 24
ADHD Predominantly Inattentive 3.13 14 8
ADHD Hyperactive Impulsive 2.13 6 9
ADHD Combined 2.13 8 7
Conduct Disorder 10.65 51 24 .001
Oppositional Defiant Disorder 11.93 45 39

Bipolar Disorder
Bipolar Disorder .57 3 1

Communication Disorders
Expressive Language Disorder 3.55 16 9
Mixed Receptive-Expressive LD 1.56 7 4
Phonological Disorder 2.41 7 10

Depressive Disorders
Dysthymic Disorder 15.20 31 76 .001

Eating Disorders
Anorexia Nervosa 2.70 3 16 .01
Bulimia Nervosa 3.69 10 16

Learning Disorders
Disorder of Written Expression 7.24 37 14 .001
Mathematics Disorder 7.24 19 32
Reading Disorder 8.95 43 20 .001

Pervasive Developmental Disorders
Asperger's Disorder .28 2 0
Autistic Disorder 1.28 6 3

Tic Disorders
Tic Disorder (Motor & Vocal) 13.64 47 49
Tic-Motor 6.25 21 23
Tic-Vocal 7.39 26 26
Tourette's Disorder 4.26 14 16

Table 3. Frequency distribution of positive screens self-reported by each participant of the Positive Screen group (n=338)

Number of
Positive Screens
Frequency %
Frequency
1 156 46.15
2 56 16.57
3 47 13.91
4 25 7.40
5 18 5.32
6 12 3.55
7
8+ 11
13 3.25
3.85

Table 4. Percentage rank order of comorbidity among the disorders.

Disorders (Rank Ordered) Percentage of comorbidity

MRE 48.3%
DD 45.1%
ODD 44.4%
ADHD 37.9%
CD 33.2%
PD 31.5%
GAD 30.7%
TD 30.6%
MD 30.4%
DWE 30.2%
RD 29.8%
SAD 27.1%
OCD 25.8%
TicD 23.2%
PTSD 20.8%
ELD 19.1%
AN 16.7%
BN 13.3%