Investigating the construct of ADHD: Issues related to factor structure in Korean students

The purpose of the present study was to accomplish three tasks. The first task was to examine the reliability and validity of a diagnostic tool for identifying children with Attention Deficit Hyperactivity Disorder (ADHD) in a Korean population, as described in the Diagnostic and Statistical Manual of Mental Disorders-IV-Text Revision (DSM-IV-TR). Evidence of reliable and valid scores, based on DSM-IV-TR diagnostic definitions of ADHD, was necessary to accomplish the other two tasks. The second purpose of the study was to explore whether the current version of the DSM-IV-TR, which consists of two dimensions of inattention and hyperactivity-impulsivity, was appropriate for describing the psychological and behavioral problems of Korean children with ADHD. The third purpose of the study was to examine gender differences in the factor structures of the DSM-IV-TR in Korea, between boys and girls with ADHD.

The DSM-IV-TR is the most commonly used manual in the United States to identify students with ADHD. Although DSM-IV-TR criteria have been used in research on ADHD with Korean school-age children, psychometric characteristics of ADHD criteria described in the DSM-IV-TR have not been examined. This missing information is imperative for quality research. The DSM-IV-TR used in this study contains 18 ADHD criteria for children's problematic behaviors manifested in inattention and hyperactivity-impulsivity.

A questionnaire distributed to 48 elementary school teachers asked them to rate their students' behaviors. The questionnaire was a 5-point scale to indicate the degree of severity of the problems the teachers experienced with the students. A total of 1,663 children, 904 males and 759 females, from grades one to six in eight elementary schools located in three cities in South Korea were rated.

One way to show evidence of a valid score by the diagnostic definition of ADHD described in the DSM-IV-TR is to show that the measures generated from the DSM-IV-TR are related to results of other tools that measure the same or similar variables. To demonstrate the concurrent validity of the DSM-IV-TR criteria, the author also administered the Attention-Deficit Hyperactivity Disorder Test (ADHDT), another tool measuring ADHD. Another way to show evidence of valid scores of the diagnostic symptoms of ADHD based on the DSM-IV-TR is to reveal that they were exactly measuring traits related to behavioral and psychological characteristics of ADHD. To demonstrate the construct validity of the DSM-IV-TR criteria, the author tried to discover evidence shown by previous studies. Previous studies related to ADHD have documented that individuals with ADHD have frequently been found to have comorbid Oppositional Defiant Disorder (ODD) and to experience more disciplinary and peer problems. As a result, to support the evidence of construct validity of the ADHD rating scale based on the DSM-IV-TR, measurement of ODD in the DSM-IV-TR and questions asking about disciplinary problems and peer problems were used. The author has completed the preliminary analysis on reliability of the variables.

For the data analysis, scores of reliability and validity of the diagnostic definition of ADHD as described in DSM-IV-TR were examined by using Pearson correlation coefficient, Cronbach alpha, and Confirmatory Factor Analysis (CFA). CFA is an appropriate statistical method to answer questions on the appropriateness of the factorial structure of ADHD in the DSM-IV-TR and the gender difference in the configural structure between boys and girls.

Scores associated with the diagnostic definition of ADHD as described in the DSM-IV-TR in a Korean population turned out to be internally stable and valid from teachers' reports. Next, findings from CFA showed that both the two-factor (inattention and hyperactivity/impulsivity) and the three-factor model (inattention, hyperactivity and impulsivity) of ADHD fit the data well. However, the three-factor model showed slightly higher scores in NFI, TLI, and CFI values and slightly lower scores in RMSEA value. Last, CFA exploring the differences in factor structure across gender revealed that the three-factor model of ADHD fit the data well for boys in all the sample sizes. However, it fit the data well for girls in only the whole population group that considered the values of NFI, TLI, and CFI, but not RMSEA. The three-factor model of ADHD appeared to be the best fit to the data in Korean elementary boys but only satisfied the three incremental indices, NFI, TLI, and CFI values, in the girls' group.

Factor structures of ADHD need to be explained under theoretical assumptions. Barkley's (1997) recently developed hybrid neuropsychological model has been accepted as a unifying way to explain the nature of ADHD. The DSM-IV-TR as a tool to diagnose ADHD was discussed from the perspective of Barkley's hybrid model.