N. Bleichrodt

Twin–singleton differences in intelligence?

The twin method has been criticised for its alleged non-generalisability. When population parameters of intellectual abilities are estimated from a twin sample, critics point to the twin-singleton differences in intrauterine and family environments. These differences are suggested to lead to suboptimal cognitive development in twins. Although previous studies have reported twin-singleton differences in intelligence, these studies had two major drawbacks: they tested young twins, and twins were compared with (genetically) unrelated singletons. To test accurately whether twin-singleton differences in intelligence exist, a group of adult twins and their non-twin siblings were administered the Dutch WAIS-III. The group was large enough to detect twin-singleton differences of magnitudes reported in earlier investigations. The data were analysed using maximum likelihood model fitting. No evidence of differences between adult twins and their non-twin siblings on cognitive performance was found. It is concluded that twin studies provide reliable estimates of heritabilities of intellectual abilities which can be generalised to the singleton population.

Iodine Deficiency, Implications for Mental and Psychomotor Development in Children1

Endemic goiter and endemic cretinism are an important national health problem in various countries. Although several ecological factors may contribute to the development of endemic goiter (1–3), iodine deficiency is assumed to be the major one (4). This assumption is supported by the positive effects of prophylactic measures- especially the administration of iodinated salt and iodized oil — on the mental and physical development of people from severely iodine-deficient areas. For its hormone production, the thyroid gland requires a certain amount of iodine, which is taken in the form of iodinated salts present in food and drinking water. Severe and prolonged iodine deficiency frequently leads to an enlargement of the thyroid gland (goiter), the volume of which may vary strongly. Such an enlargement is found more often in females than in males (5–9). Goiter is usually defined in the terms proposed by Perez et al. (10), a definition later adopted by the World Health Organization in a slightly different wording: “a thyroid gland whose lateral lobes have a volume greater than the terminal phalanges of the thumbs of the person being examined will be considered goitrous”. The volume of the enlargement is usually defined according to a four-graded division, ranging from OB (detectable only by palpation and not visible even when the neck is fully extended) to III (visible from a long distance).

Does Cultural Background Influence the Intellectual Performance of Children from Immigrant Groups

Summary: This paper addresses both the construct validity and the criterion-related validity of the “Revisie Amsterdamse Kinder Intelligentie Test” (RAKIT), which is a cognitive ability test developed for primary school children. The present study compared immigrant primary school children (N = 559) and Dutch children (N = 604). The mean scores of Surinamese/Netherlands Antillean, Moroccan, and Turkish children differed from each other and were lower than those of the Dutch children. Comparison of the test dimensions showed that group differences with respect to the construct validity were small. We found some item bias, but the combined effects on the sum score were not large. The estimate of general intelligence (g) as computed with the RAKIT showed strong predictive validity for most school subjects and standardized achievement tests. Although some criteria revealed significant prediction bias, the effects were very small. Most of the analyses we performed on differences in test scores and differences ...

Absence of neuropsychological sequelae following cerebral malaria in Gambian children

Cerebral malaria causes major neurological sequelae in a proportion of survivors and may lead to neuropsychological sequelae in children who seem to have made a good recovery. If this is the case, cerebral malaria could have a dramatic impact on the development of thousands of African children. The present study was carried out to provide information on the incidence and type of neuropsychological sequelae in children who survive the disease without major neurological sequelae. A matched case-control study design was used in which 36 pairs of children were assessed. The cases had been treated for cerebral malaria a mean of 3.4 years before testing. No evidence of a serious long-term impact on most assessed neuropsychological functions was found in these children. Only in the balance test did cases perform less well than their matched controls, but the difference between the 2 groups was only of borderline significance. These findings suggest that the long-term impact of cerebral malaria on the development of children who recover without major neurological sequelae is not as serious as had been feared.

Measuring personality traits in the classroom.

In this article, a personality model for the description of childrens classroom behaviour is the main focus of interest. It is questioned whether the Five‐Factor Personality Model can be used as an organizational structure for the description of personality characteristics in the field of educational practice. Two groups of Dutch school children (N=1296 and N=367), 4–12 years old, were rated by their teachers on scales of the School Behaviour Checklist–Revised (SCHOBL‐R, we would like to thank Dr J. N. Zaal for his contribution to the construction of and research with the original School Behavior Checklist (SCHOBL). We also wish to thank Professor G. A. Kohnstamm for his suggestions and comments on the first draft of this article). Analysis of the scales produced four meaningful and identical components in both samples: Extraversion, Attitude towards School Work, Agreeableness, and Emotional Stability. The factorial structure of the scales remained stable over age as well as sex. Boys and girls were rated by their teachers as having different attitudes towards school work, and as differing on emotional stability and agreeableness. The items of the school behaviour checklist were then analysed in the context of other personality scales, leading to the conclusion that the four scales of the SCHOBL‐R can be interpreted in terms of four of the five personality dimensions of the Five‐Factor Model. The strong relationship between the contents of the different scales used in this analysis supports the idea that the Five (Four) Factor Model is a valid model for the description of individual differences in Dutch school children. Copyright