**2. Aims of epidemiological research**

The epidemiology of childhood psychopathology includes the following aims (Costello & Angold, 1995):


scales.

of categorical diagnoses.

cultures (Achenbach & Rescorla, 2007).

as assessment, diagnostic principles, and morbidity criteria.

**4.2 Methodological Issues** 

The Epidemiology of Child Psychopathology: Basic Principles and Research Data 141

called *period prevalence* (e.g. 6-month prevalence or lifetime prevalence) is frequently used in prevalence studies of child psychiatric conditions. There are two types of studies determining the prevalence of child psychopathology: (1) those that produce prevalence rates of psychiatric diagnoses, usually based on DSM (Diagnostic and Statistical Manual of Mental Disorders) criteria, and (2) those that generate scores on psychiatric symptom rating

Many studies that determined prevalence rates of DSM diagnoses in general population samples of children have been conducted. Costello, Egger and Angold (2005), Roberts, Attkisson and Rosenblatt (1998), Verhulst (1995), and Waddell et al. (2002) provided reviews. Despite huge research efforts and many children involved, comparisons between these studies are seriously hampered by large differences in design and methodology including differences in sample size, age of children, assessment and sampling procedures, and case definition. Even for studies conducted in countries comparable in language, culture, and availability of services, differences in prevalence rates were extremely large and ranged from 10% to 20% (Waddell et al., 2002). It is more likely that these differences reflect variations in methodology than differences in true prevalence. Methodological variations and the lack of standardization among studies seriously limit the value of prevalence figures

The second approach, the use of rating scales for assessing parent- or self-reported emotional and behavioural problems of children in representative general population samples, is less vulnerable to methodological differences. This approach produces problem scores on continuous scales and does not generate prevalence rates for categorical diagnoses. Often, statistical criteria are used for distinguishing between cases and non-cases. Although dividing lines for caseness may be rather arbitrary, there are epidemiological methods for selecting effective cut-off points. However, prevalence figures will vary with the statistical criterion and cannot be used as absolute population prevalence measures without relating them to similar measures for other populations or subpopulations (Verhulst, 1995). In two recent multicultural prevalence studies, parents' reports and youths' self-reports of problems for children using the Child Behavior Checklist (CBCL) in 31 cultures, and the Youth Self-Report (YSR) in 24 cultures, were compared (Rescorla et al., 2007a; b). It was found that, when the same standardized assessment procedures are used for assessing children from different cultures, cultural differences per se do not lead to big differences in reported problems. Instead, individual differences within each cultural group are bigger than differences between the average scores obtained in different cultures. Assessment procedures with good cross-cultural track records and appropriate translations that capture individual differences in reliable and valid ways are apt to reflect the mental health needs of children that are robust across

A number of methodological issues of child psychiatric prevalence studies will be considered for better understanding the results of these studies. Issues that pertain to general epidemiological methodology, such as sampling and data analysis, will not be discussed here. The focus will be on issues that are specific to child psychopathology, such


Epidemiology does not refer to a single scientific discipline or the use of one specific methodology. Instead, epidemiology derives and integrates concepts and methods from other areas such as biology, statistics, and sociology. In epidemiology, the combination of measurement principles and statistics is used for the development and testing of diagnostic assessment procedures. When applied to psychological concepts, the combination of measurement and statistics is called psychometrics. In epidemiology of child psychopathology, psychometric principles play an important role. A number of specialized areas that are derived from classical epidemiology are relevant to child psychopathology, including clinical epidemiology, genetic epidemiology, and pharmaco-epidemiology. Clinical epidemiological studies concern the development and application of diagnostic and screening tests, the prognosis of disorders, the effects of treatment and clinical decisionmaking.
