Risk Factors For Attention Deficit/hyperactivity Disorder

National Institute Of Environmental Health Sciences

Investigators

Linked publications & trials

Abstract

The prevalence of and risk factors for Attention Deficit Hyperactivity Disorder are being investigated in a population-based study carried out in Johnston County, North Carolina. Through the cooperation of the Johnston County schools, all elementary school age children in the county were studied. With parental permission, teachers completed behavior rating evaluations for children in their classroom. All children classified as potentially having ADHD according to teacher responses or reported by parents to be taking medications were eligible for further study, along with a random sample of all other children. Parent interviews obtained information on child behavior, prenatal and childhood exposures, parental occupational exposures and other factors potentially related to risk for ADHD. We combined parent and teacher information to estimate the prevalence of ADHD among elementary school children using a scale based on DSM-IV criteria. We asked parents of 7333 children in grades 1 through 5 attending 17 public elementary schools whether their child had ever been given a diagnosis of ADHD by a psychologist or physician and whether their child was currently taking medication to treat ADHD. Based on results from the first year of the study, according to parental reports, 43 children (12%) previously had been diagnosed with ADHD by a health professional. Thirty-four children (9%) were taking ADHD medication. Forty-six children met study case criteria for ADHD based on combined teacher and parent reports. After adjusting for non-response, the estimated prevalence of treated or untreated ADHD combined was 16%. The prevalence estimate based on the full sample is about 12%, lower than in the first year but still greater than published reports based on DSM-IV criteria. In the overall study, parents of 6099 children (83%) provided information on medication use. Of these, 607 children (10%) had been given an ADHD diagnosis, and 434 (7%) were receiving ADHD medication treatment (71% of the diagnosed children were receiving medication). Treatment rates varied by sex, race/ethnicity, and grade. If treatment patterns observed in this study are representative, the public health impact of ADHD may be underestimated. [unreadable] [unreadable] Research on the correlates of ADHD subtypes has yielded inconsistent findings, perhaps because the procedures used to define subtypes vary across studies. We examined this possibility by investigating whether the ADHD subtype distribution in our study was sensitive to different methods for combining informant data. We found substantial differences in the distribution of ADHD subtypes depending on whether one or both sources were used to define the subtypes. When parent and teacher data were combined, the procedures used substantially influenced subtype distribution. ADHD subtype distribution is clearly sensitive to how symptom information is combined. [unreadable] [unreadable] Since we adapted existing instruments to conduct our study, we assessed the psychometric properties of the modified instruments. Specifically, we evaluated the impact of changing the response labels of a teacher rating scale. For parents, the Diagnostic Interview Schedule for Children, which asks whether each of 18 symptoms occurred "often" in the past year, was used. For teachers, most scales use a 4-point scale, with often and very often as the two highest categories. To make the two instruments more compatible, we created a teacher rating scale with often as the highest category. Teachers rated more than 6,000 elementary school students using this instrument. Some teachers completed ratings using both questionnaire formats. We found the new scale's internal consistency, convergent validity, and test-retest reliability to be excellent. The factor structure is consistent with established DSM-IV-based instruments, although response category choices influence the proportion of children exceeding symptom and impairment thresholds. Altering the response scale does not degrade the psychometric properties of the instrument but makes important differences in the sample.[unreadable] [unreadable] We are now working to characterize the overall prevalence of AHDD and identifying pregnancy-related factors as well as environmental exposures such as lead that may contribute to risk of ADHD. Dr. Rowland (former NIEHS lead investigator) has begun to follow-up the children who were studied to evaluate persistence of symptoms and outcomes among children with various subtypes of ADHD.