Mental health of young people in Australia

2 Study sample and methodology

Page last updated: October 2000

What are mental health problems and mental disorders?
Who participated in the survey?
How were children and adolescents assessed?
Terms and conventions used in this report

What are mental health problems and mental disorders?

Terms such as mental health problems, mental disorder and emotional and behavioural problems do not have exact definitions. They are commonly used to describe alterations in thinking, mood or behaviour that are associated with distress or impaired functioning. There are a number of different types of mental health problems and mental disorders, and each consists of a different combination of emotional and behavioural problems.

In this report, children and adolescents were considered to have a mental health problem if the number of emotional and behavioural problems they were experiencing was in the range typically reported for children and adolescents attending mental health clinics (Achenbach, 1991a; Achenbach, 1991b). Mental health problems were identified by having parents and adolescents complete questionnaires asking about a large number of emotional and behavioural problems that occur in childhood and adolescence (Achenbach, 1991a; Achenbach, 1991b).

Mental disorders are conditions characterised by clinically significant sets of symptoms or emotional and behavioural problems associated with personal distress and impaired functioning, as described in the Diagnostic and Statistical Manual of Mental Disorders, 4th edition (American Psychiatric Association, 1994). Three child and adolescent mental disorders were investigated in this survey: Depressive Disorder, Conduct Disorder and Attention-Deficit/Hyperactivity Disorder. These disorders were chosen by the National Collaborating Group because they are known from previous studies to be prevalent in the community and because they have great significance for child and adolescent health in Australia. Mental disorders were identified using face-to-face interviews conducted with parents by trained interviewers using the Diagnostic Interview Schedule for Children Version IV (Shaffer, Fisher, Lucas, Dulcan, & Schwab-Stone, 2000).
Top of page

Who participated in the survey?

We used a multistage sampling scheme to recruit a representative sample of 4,500 children aged 4 to 17 years (Appendix C). Children were recruited by interviewers who approached randomly selected households chosen in proportion to the population of each state or territory. The identified households were also distributed proportionally across metropolitan and non-metropolitan areas (with the exception of the Northern Territory, where only children living in metropolitan areas were recruited). Children under 4 years of age were not included because the problems of this group differ from those of older children and adolescents, as do the methods required to assess them. The upper age limit of 17 years was determined by the lower age limit of participants included in the Australian survey of adults (Andrews, et al., 1999).

A participation rate and a response rate for the study were calculated as follows. The participation rate was calculated by dividing the number of households with a child aged 4 to 17 years that participated in the survey by the total number of households which were contacted and identified to contain a child aged 4 to 17 years. The participation rate was 86%. The response rate was calculated by dividing the number of participating households by the total number of households that were initially identified as potential participants in the survey. No contact was made with a family member in a number of the identified households, however, and it was estimated that 19% of these households would have contained a child eligible to participate in the survey. After an adjustment to take these children into account, the response rate for the survey was 70%. The major reason for the difference between the response rate and the participation rate was a failure by interviewers to make contact with a number of the identified households before selecting a replacement household.

Two approaches were used to identify possible biases in the selected sample. First, the demographic characteristics of children, adolescents and families who participated in the study were compared with those of the total Australian population from which they were selected. Second, scores on the behaviour checklists used in the survey were compared with the scores on the same checklists reported in the Western Australian Child Health Survey (Zubrick et al., 1995) and with scores reported in the manuals that describe these checklists (Achenbach, 1991a; Achenbach, 1991b). The results of these comparisons suggest that the sample of 4 to 17 year olds in the survey is representative of the total population of children and adolescents aged 4 to 17 years in Australia.

Accurate prevalence estimates are not possible for some groups within the Australian population. In part, this is because they are not represented in large enough numbers in the study sample. For example, the survey provides only limited information about Aboriginal and Torres Strait Island children and adolescents, a group that represents approximately 3% of the total Australian population. Although the number of children and adolescents of indigenous background included in the survey is consistent with that of the general population, it is too small for us to be sure that the information reflects the characteristics of all indigenous children and adolescents. Furthermore, a different type of study using culturally sensitive methods may be required to assess problems in this population.

The survey provides only limited information about the mental health of children and adolescents living in non-English-speaking families. There are two reasons for this. First, parents needed to have sufficient competence in English to complete the structured interview and questionnaires. Second, because there are relatively few non-English-speaking families in the population, there were not enough children and adolescents in the survey to provide an accurate picture of the mental health of all children and adolescents living in these families.

The survey was also unable to assess the prevalence of mental health problems in certain other groups, such as homeless young people and those in hospitals or detention centres. These groups could not be included because the survey procedure was based on households. It should be noted that if these groups had been included, it is likely that a higher prevalence of mental health problems would have been identified.
Top of page

How were children and adolescents assessed?

Information from parents, teachers, children and adolescents can be used to assess the mental health of participants in surveys of child and adolescent mental health. In the present survey, information was obtained from the parents of all participants and also from adolescents aged 13 to 17 years. This approach was adopted because we had insufficient resources to contact the teachers of all participants and were able to conduct a face-to-face interview with only one member of each household. This interview was conducted with parents. Parents and adolescents also completed a self-report booklet of questionnaires.

There is considerable evidence that parents, teachers, and children and adolescents differ in their perceptions of childhood and adolescent mental health problems (Achenbach, McConaughy, & Howell, 1987). Thus, it is likely that a higher prevalence of problems would have been identified if problems identified by all three categories of informants had been added together to form the prevalence estimates.

(i) Use of behaviour checklists to identify mental health problems

The checklists employed in the survey asked about a wide range of emotional and behavioural problems that occur in childhood and adolescence (Achenbach, 1991a; Achenbach, 1991b). Responses to these questions were combined to produce behaviour problem scores that rated the number and severity of emotional and behavioural problems in different areas (Appendix A). In each area, children and adolescents were considered to have a mental health problem if their score on the relevant behaviour problem scale was in the range typically reported for those of the same age and gender attending mental health clinics. Such scores were said to be in the 'clinical range' on each behaviour scale.

As noted by Achenbach (1991a), referral to a mental health clinic is not an infallible criterion of a child's need for help. Nor can it be assumed that all children referred to clinics have mental health problems. Some children, for example, are referred to mental health clinics because of family problems rather than because of mental disorders. However, despite its limitations, clinic referral does provide a useful criterion for estimating the number of children in a community who are experiencing high levels of mental health problems.

It is also important to recognise that the threshold scores for inclusion in the clinical range vary with age and gender. The scores selected as threshold points are those that best discriminate 'referred' from 'non-referred' children within each age and gender group (Achenbach, 1991a; Achenbach, 1991b).

The key aim of this survey was to identify the number of children and adolescents with a high level of emotional and behavioural problems. Thus, the results in the main body of the report focus on the percentage of children or adolescents in each age and gender group who scored in the clinical range on the various behaviour problem scales. Information about typical levels of emotional and behavioural problems, however, is provided by the average behaviour problem scores on the survey checklists. These are shown for each age and gender group in Appendix A.
Top of page

(ii) Use of the Diagnostic Interview Schedule for Children to identify mental disorders

The three child and adolescent mental disorders investigated in this survey were identified by means of face-to-face interviews conducted by trained interviewers using a structured diagnostic interview, the Diagnostic Interview Schedule for Children, Version IV (Shaffer et al., 2000). The Diagnostic Interview Schedule is designed to identify more than 30 mental disorders that occur in childhood and adolescence.

Parents of all participating children and adolescents from 6 to 17 years completed the interview. The lower age limit was necessary because the Diagnostic Interview Schedule is not suitable for use with children younger than 6 years of age. Face-to-face interviewing is expensive, however, and it is also burdensome for parents and children. For example, it takes parents an average of 70 minutes to complete the Diagnostic Interview Schedule if the complete interview is employed. To address these problems, the Diagnostic Interview Schedule employs a modular format that makes it possible to limit the number of mental disorders assessed in a particular survey. For this survey, we utilised the modules for Depressive Disorder, Attention-Deficit/ Hyperactivity Disorder, and Conduct Disorder.

Regrettably, we were unable to include Anxiety Disorders in the survey. The assessment of these disorders with the Diagnostic Interview Schedule is complex, and their inclusion would have required another group of disorders to be dropped. The exclusion of Anxiety Disorders is unfortunate, because other surveys have shown these disorders to be relatively common among children and adolescents (Shaffer et al., 1996). It also should be noted that if a wider range of disorders had been investigated, a higher prevalence of mental disorders would have been identified in the survey.

The criteria used in the Diagnostic Interview Schedule to identify the three mental disorders are similar to those in the Diagnostic and Statistical Manual of Mental Disorders, 4th edition (DSMIV) (American Psychiatric Association, 1994). However, there are some important differences. First, children who meet the criteria for a DSM-IV diagnosis must exhibit clinically significant impairment in social, academic or occupational functioning. Although the Diagnostic Interview Schedule asks about impairment, the responses are not currently used in the calculation of prevalence rates because this section of the scoring algorithms is considered experimental. This means that some children or adolescents identified as having a disorder in the survey may not meet all the formal diagnostic criteria described in the DSM-IV. Second, we could not determine whether children had other disorders that preclude the diagnosis of one of the disorders reported in this survey. For example, the DSM-IV criteria require that children not be diagnosed with Attention-Deficit/Hyperactivity Disorder if their symptoms occur exclusively during the course of a Pervasive Developmental Disorder, Schizophrenia or other Psychotic Disorder, or if their symptoms are better explained by another mental disorder (e.g., Mood Disorder, Anxiety Disorder, Dissociative Disorder, or a Personality Disorder). Similarly, children should not be diagnosed with a Major Depressive Disorder if their symptoms are due to the physiological effects of a substance (e.g., a medication) or to a general medical condition. If these criteria had been applied, it is possible that a lower prevalence of some mental disorders may have been found in the present survey.
Top of page

(iii) Information obtained from parents

During the face-to-face interview, parents completed the Diagnostic Interview Schedule. They also described the use by children and adolescents of a wide range of professional services during the six months prior to the survey, the type of help provided for children and adolescents attending services, and any barriers that hindered access to services. Parents also completed a questionnaire booklet that asked them to respond to questions in the following areas:
  • Mental health problems: Mental health problems were identified using the Child Behaviour Checklist (Achenbach, 1991a). This checklist was chosen because it provides information about a range of child and adolescent mental health problems, it has been widely used in comparable studies in other countries, and it is easy for parents to complete. Children and adolescents were considered to have a mental health problem if the number of emotional and behavioural problems parents reported on the relevant Child Behaviour Checklist scale was in the range typically reported for children and adolescents attending mental health clinics (Achenbach, 1991a).

  • Degree of disability: The concept of health-related quality of life was utilised to assess the level of disability experienced by children and adolescents. It was measured using the Child Health Questionnaire, which assesses the functioning of children in a range of areas, including physical health, limitations in school and peer activities, and the impact of children's health on parents and families (Landgraf, Abetz, & Ware, 1996). Parents of children aged 6 to 17 years completed the Child Health Questionnaire. The lower age of 6 years was chosen because assessment in several domains is based on children's school functioning, and 5-year-olds have not started school in some states of Australia.

(iv) Information obtained from adolescents

Adolescents aged 13 to 17 years completed a questionnaire booklet that asked them to respond to questions in the following areas:
  • Mental health problems: Mental health problems were identified using the Youth Self-Report (Achenbach, 1991b). The Youth Self-Report is very similar to the Child Behaviour Checklist but is designed for completion by adolescents. It was considered important to obtain information directly from adolescents about their mental health problems, as they may have a different perspective than their parents (Achenbach et al., 1987).

  • Degree of disability: Adolescents' perceptions of their health-related quality of life were assessed using the adolescent version of the Child Health Questionnaire. This version of the questionnaire is similar to the version completed by parents but is designed for completion by adolescents (Landgraf et al., 1996).

  • Health-risk behaviour: Information about health-risk behaviour (e.g., drug use and suicidal behaviour) was obtained from adolescents using relevant items from the Youth Risk Behaviour Questionnaire. The Youth Risk Behaviour Questionnaire was developed by the Centers for Disease Control and Prevention in the United States to identify health-risk behaviour in high school students (Brener, Collins, Kann, Warren, & Williams, 1995).

  • Service utilisation: Adolescents were asked whether they had received help for mental health problems or problems with their physical health during the last six months. They were also asked to identify barriers that may have hindered access to services.
Top of page

Terms and conventions used in this report

In the interests of readability and conciseness, we have presented many of the results in the report as graphs or figures and have omitted descriptions of levels of statistical significance or confidence intervals. However, significant and substantive differences in the prevalence of mental health problems, the health-related quality of life of children and adolescents, and patterns of service utilisation are drawn to the attention of readers in the text.

In addition, we have tried to avoid repetition by reporting only one set of results when there were no major differences between the reports from parents and adolescents. Similarly, if there were no important differences between reports describing children and adolescents, the results describing the two age groups were combined.

The estimates of prevalence for the three mental disorders are 'one year' estimates. That is, they estimate the number of children and adolescents who met the criteria for one or more of the disorders during the year prior to the study. The estimates were weighted for each individual's responses according to the degree to which that individual's demographic grouping was under- or over-represented in the final sample. Details of the procedure used to obtain the survey weights are provided in Appendix C.

The term parent is used to describe the primary caregiver who completed the interview/ questionnaire. In most cases this was the mother (84%), but in some cases the father (12%) or another person or relative (1%) was the primary caregiver. In 3% of cases, both parents completed the interview/questionnaire.

In some areas, the questionnaires that were used to gather information about mental health problems, health-related quality of life or health-risk behaviours contained similar questions. The duplication of these questions raises the possibility that some significant relationships identified in the study could have arisen simply because questionnaires assessing different health constructs contained similar questions. To address this issue, all the analyses were repeated after the removal of questions that were similar on two or more questionnaires. In no cases did the presence of similar questions on two or more questionnaires influence the pattern of findings.