Soo Hyun Rhee1, Irwin D. Waldman1, David A. Hay2, & Florence Levy3
Several recent studies have examined whether sex is a moderator of the magnitude of genetic and environmental influences on ADHD. Most of these studies have examined ADHD as a unidimensional construct (e.g., DSM-III-R ADHD) and have not addressed how results may differ for the DSM-IV symptom dimensions of inattention and hyperactivity/impulsivity. In this paper, we contrast several alternative models that test for sex differences in the magnitude of genetic and environmental influences on inattention and hyperactivity/impulsivity. The participants are 2043 3- to 15-year-old twin pairs and 348 3- to 18-year-old sibling pairs from Australia. Zygosity was determined from mothers' responses to questions regarding the physical similarity of the twin pairs. Data on DSM-IV ADHD symptoms were gathered from a questionnaire completed by mothers of the twins. We compare the fit of a number of alternative sex difference models, including the homogeneity model, the heterogeneity model, the scalar model, and the general sex-limitation model. The implications of the best-fitting models are discussed.
Address: mailing address - Department of Psychology, Emory University, Atlanta, GA, 30322, phone - (404) 727-2741, fax - (404)727-1284, e-mail - soorhee@social-sci.ss.emory.edu
1Department of Psychology, Emory University, Atlanta, GA 30322. 2Department of Psychology, Curtin University, Perth, Western Australia, Australia. 3Department of Child and Adolescent Psychiatry, The Prince of Wales Children's Hospital, High Street, Randwick, NSW 2031, Australia.