Following are some technical details about the Gothenburg study of Christopher Gillberg.
In the Gothenburg study, all preschool teachers in the city of Gothenburg, Sweden, were asked to answer a series of questions about each of their students. The children were then age 6–7 (born 1971). The purpose of the questioning was to identify children with certain potential psychiatric problems. Based on the answers to the questions, children with potential problems were classified into either a “high-index” or a “low-index” group.
In the investigation, there were 22 children (14 boys and 8 girls) in the high-index group and 60 children (52 boys and 8 girls) in the low-index group. The children in the index groups were compared with a randomly-selected control group. The control group ultimately consisted of 59 children (29 boys and 30 girls). There were thus 141 children in total.
Each of these children was then given a thorough examination (by two psychiatrists, a physiotherapist, a neurologist, and a psychologist). Of the 141 children, 42 (33 boys and 9 girls) were diagnosed as having DAMP/MBD. Of the 42, 40 were in the index groups (18 in the high-index group) and 2 were in the control group. Also, 29 of the 82 children in the index groups were diagnosed as having no sign at all DAMP/MBD.
The children were later examined at ages about 10, 13, 16, and 22. The 29 children in the index groups who had no sign at all of DAMP/MBD, however, were officially excluded from further studies. Thus the total number of children studied after age 7 was 141 − 29 = 112. (In practice, some of those 112 children moved to other countries, or were otherwise unavailable; so the actual number was slightly less.)
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Rydelius P.-A. (2000), “DAMP and MBD versus AD/HD and hyperkinetic disorders”, Acta Pædiatrica, 89: 266–268. doi: 10.1080/080352500750028375.