Genetic and environmental influences on pupil performances.

The results presented in this paper are part of a current comparative study of genetic and environmental influences in three educational settings: Stockholm, Jerusalem and the Israeli kibbutz. We specifically wanted to investigate whether a more restrictive educational setting would decrease genetic influences. Here we report on comparisons of cognitive performance measures at several time points for twins/controls, boys/girls and within-pair similarity in MZ, DZ and controls. The tests used were the Raven Progressive Matrices, verbal, reading comprehension and arithmetic. The results show no differences between twins and controls, whilst gender differences seem to be smallest in the Stockholm sample and largest in Jerusalem. A pattern of genetic influences on cognitive performance was also clearly visible in Jerusalem. In Stockholm shared environmental influences at home and at school seemed even stronger than in the kibbutz. No consistent differences were found between tests or occasions.

Nurse education and professional work: transition problems?

The purpose of this study was to investigate the transition from a 3-year nursing programme to a professional role as a nurse. Eight subjects kept diaries during 2 months. Data were recorded in a notebook and categorization of data was based on interpretation by two independent persons. Results are presented in relation to the different categories which became evident from the diaries. A common problem for newly registered nurses was the management of paperwork. The more administrative work the nurses had, the less time they were able to spend on patient-oriented activities. Generally, the nurses felt uncertain about care of patients with serious illnesses. All the nurses experienced a high workload and also reported difficulties in feeling relaxed during their off-duty time. Additional difficulties encountered included knowing the kind of tasks they were able to delegate to assistant nurses, and deciding on when it would be appropriate to call for a physician. Further research is needed to provide a better understanding of the relevance of nurse education for the management of the work situations encountered by newly registered nurses.

Life situation, self reported health and coping ability of 35-year old twins and controls--a follow-up of a longitudinal Swedish twin study at adolescence.

During the years 1964 to 1971 a nationally representative sample of MZ and DZ twins and controls was followed through the Swedish compulsory school. The main purpose was to study physical and mental growth during puberty as well as heredity-environment influences on these growth processes. After 20 years a follow-up has been made of this sample with the purpose of investigating heredity-environment influences on life situation and self reported health at mid-life in relation to background factors collected during adolescence. 43 pairs of MZ twins, 90 pairs of DZ same sex and opposite sex twins as well 322 controls agreed to participate. A questionnaire was sent out to this group dealing with their present life situation such as family structure, economy, education and occupation. Other areas of interest were self reported health and ability to cope with their present life situation. The disadvantages found for MZ female twins at adolescence seem to persist at mid-life and ratings of school adjustment were related to coping ability as grown ups. This first report presents comparisons between twins and controls as well as males and females. To estimate heredity influences intraclass correlations for the twin pairs are calculated and for coping ability such influences seem to be quite conspicuous. Sex specific factors seem to operate regarding coping ability and satisfaction in educational choice and level. Generally, the results-indicate some advantages for the males regarding self reported life situation and health. Possible reasons for such sex differences are discussed. This study has been supported by grants from the Swedish Council for Social Research.

Individual perception of education and treatment versus actual outcome. A theoretical model exemplified by an interventional study on patients with insulin-dependent diabetes mellitus.

An educational model is presented that stresses the importance of the interaction between individual characteristics and intentional educational influences on outcome variation. This model is exemplified by an interventional study of patients with insulin-dependent diabetes mellitus who, despite long-term conventional medical treatment, had been unable to achieve satisfactory hemoglobin Alc levels. Treatment modes and their importance for understanding variations in outcomes are discussed from the interactional perspective suggested in the model.

From puberty to mid-life: a follow-up study of twins and controls.

During the years 1964 to 1971 a group of twins and a control group of singletons in the same classes, were followed from grade 3 at 10 years of age to grade 9 at 16 years of age in the Swedish compulsory school. The study was called the SLU-project (Skolöverstyrelsens och Lärarhögskolans Utvecklingsprojekt) and the main purpose was to study physical and mental growth during puberty as well as heredity and environment influences on these growth processes. Originally 323 twin pairs, MZ and DZ, and 1193 controls were included in the sample. Among the DZ twin pairs there were both same-sex and opposite-sex pairs. They were a nationally representative sample. Several kinds of information were collected, such as, a) Physical measurements (height and weight measurements, menarche, ratings of secondary sex characteristics); b) Ability and achievement measures (intelligence tests, standardized achievement tests); c) Self ratings; d) Ratings by teachers and classmates; e) Socioeconomic background data (fathers occupation and income). For the boys, supplementary data on physical growth and mental ability was collected on enrollment to military service at the age of 18. In this pilot-study, we have made a follow-up of the original SLU-sample after 20 years. They are now in their mid-thirties. The main purpose has been to investigate if they are willing to participate in a new study on health and well-being at mid-life.

Within-pair similarity in MZ and DZ twins from birth to eighteen years of age.

This study is based on 145 pairs of twins included in a longitudinal study of a cohort of singletons born in 1953 and living in the Stockholm metropolitan area in 1963. Of these 145 pairs, 28 were classified as MZ, 103 as DZ and 14 pairs could not be classified. School achievement and ability test results have been collected for this group as well as data for the boys from physical and mental examinations on enrollment to military service. The purpose of this study was to compare within-pair similarity for MZ and DZ twins from birth onwards. There seems to be a divergent trend over time for MZ twin pairs to become more similar and DZ twin pairs to become less similar in height growth, school achievement and verbal ability. This is in accordance with previous research in this field. In relating similarity within pairs to birthweight, we found a drop in within-pair similarity for low birthweight MZ and DZ twin pairs (both twins < or = 2.500 g), but not for normal weight twin pairs. A discussion is initiated concerning methodological implications of these results.

Twins' perception of their environment: a cross-cultural comparison of changes over time.

In a previous Swedish twin project (the SLU-project), approximately 300 MZ and DZ twin pairs and controls were followed through the Swedish compulsory school from grade 3 to grade 9. Results from this study indicated an increase of genetic influences on school achievement over time for children from a permissive home environment and a decrease for children from a restrictive home environment. These types of data have generated a more general model for studying heredity-environment interaction in educational settings. To test this model, a cross-cultural comparison over time of twins and controls in the Israeli kibbutz school and in the Swedish compulsory school has been made. Restrictions on the child were originally assumed to be more apparent in the kibbutz environment.

A model of evaluation exemplified by Swedish nursing education.

In an historical perspective it can be seen that the target for educational evaluation in Swedish nursing education was changed from that of student to programme evaluation. Since education, however, is an interaction of student prerequisites and educational goal-directed influences, there is a need for a more general evaluation model. This should preferably incorporate both student and programme influences over time at different levels, from classroom to societal level. Such a model is presented here based on data from a Swedish longitudinal twin project (Fischbein, 1979). A discussion of the model is initiated from an example of a recent evaluation study made of nurse education in Sweden.

Twins: are they at risk? A longitudinal study of twins and nontwins from birth to 18 years of age.

The purpose of this study has been a comparison of a group of twins (145 paris) and a whole cohort of singletons (114,828 individuals) born 1953 and living in the Stockholm metropolitan area in 1963. The twins and singletons have been followed from birth onwards. A pertinent question is whether twins are at greater risk at birth and whether they are predisposed to below-average mental and physical growth. The results show that twins are more susceptible to lower birth weight, shorter gestation period and birth complications. These factors also seem to have a lasting effect on later physical and mental development. Monozygotic twins, twin girls, and male twins with low birth weight, seem to be particularly at risk for below-average mental and physical growth. An interaction between social background and birth weight can also be seen for the male twin group.

Simultaneous genetic analysis of longitudinal means and covariance structure using the simplex model: application to repeatedly measured weight in a sample of 164 female twins.

The simultaneous analysis of means and covariance structures is applied to longitudinal twin data. Body weight was measured on six occasions in a sample of young female MZ and DZ twins. When average body weight at the first measurement occasion, as well as the increments in weight at later occasions, are specified in the genetic part of the model that also adequately explains the covariance structure, a good fit is obtained. In this application the increase in body weight at each occasion is weighted by the square root of the genetic variance innovation terms that represent the new genetic variance entering into the process.

Qualitative and quantitative aspects on mathematics achievement in MZ and DZ twins.

Mathematics achievement test results have been collected for 22 MZ and 24 DZ same-sex twin pairs in the Swedish compulsory school. The twins were approximately 11-13 years of age and attended grades 4, 5, or 6. The twin pairs were part of a larger collaborative study between Israel and Sweden (the KAM-project). Teachers were asked how they planned and evaluated their work in the subjects Swedish and Mathematics. In addition to this, results for the twins on Maths tests given by the teachers in their regular work were collected. These tests were thus used by the teachers as an instrument to evaluate the educational process. Intrapair similarity for MZ and DZ twins has been compared for qualitative and quantitative aspects of the Maths tests. Different tests were used by the teachers but the same criteria have been used in the comparison. MZ twins are somewhat more similar than DZ twins for both the qualitative and quantitative aspects. Only one quantitative aspects, however, percentage of correct answers, shows a significant difference between the twin categories. A comparison was also made of intrapair similarity in classes, where the teachers differed according to planning and evaluation of their education. Irrespective of that, the MZ twins seemed to be more similar than the DZ twins in number of correct answers on the Maths tests. Educational implications are discussed.

Permissiveness-restrictiveness for twins and controls in two educational settings: The Swedish compulsory school and the Israeli kibbutz.

In a previous longitudinal twin project a model was developed for studying heredity-environment interaction. One important environmental dimension in this model is permissiveness-restrictiveness. The purpose of the present study has therefore been to investigate perceived and imposed restrictiveness at the societal and classroom level and possible interactional effects on pupil behavior. Results are reported from grade 4 to grade 6 in Israeli kibbutzim and Swedish compulsory school. One major finding is that no systematic differences have been found between twins and controls in the two countries. In both Swedish schools and Israeli kibbutzim permissiveness-restrictiveness will vary depending upon perspective (perceived or imposed) and upon content (type of subject or rule-breaking activity). Preliminary within-pair comparisons for the Swedish twins are reported for different types of test results. In agreement with the model, logical abstract thinking as well as reading and mathematics achievement seem to be less influenced by hereditary factors in a restrictive educational setting than in a permissive one.

What is it like to be a parent of twins?

A questionnaire was given to parents of twins concerning their perceptions of dependency and similarity in their twin children. Also, the parents were asked if they tried to influence their children to become more dissimilar. 70 same-sex twin pairs (35 MZ and 35 DZ) were included in the study and a questionnaire was sent both to the mother and the father of the twins. The twins were approximately 12 years old and attended grade 4, 5 or 6 in the Swedish compulsory school. Results indicated that parents consider MZ twins to be dependent upon each other and to spend more time together. This was especially evident for girls. If the twins had a free choice they would also tend to choose similarly. This trend was also more pronounced for the MZ girls. Irrespective of zygosity, most parents reported that they did not try to influence their children. In the case of MZ twins this will probably make them become more similar over time. Differences between maternal and paternal answers tended to be nonsignificant.

Nature-nurture interaction in different types of school environments. A longitudinal study.

A model of nature-nurture interaction in school situations emanating from a longitudinal Swedish twin project is presented. This model implies that interactional effects measured by MZ-DZ within-pair comparisons over time are related to the type of behavior studied, as well as teacher and pupil influences at different levels. In a more permissive and stimulating school situation, hereditary factors are hypothesized to be more influential (decisive for behavioral variation) than in a more restrictive and nonstimulating situation. A study of such interactional effects will require longitudinal measurements of pupil behavior as well as teacher and parental influences. To acquire a variation in permissiveness/restrictiveness and stimulation/nonstimulation at the societal level, comparisons are made between twins attending grade 4-6 in compulsory schools in Sweden and twins of the same age attending Israelian Kibbutz schools.

Multivariate analysis of genetic and environmental influences for longitudinal height and weight data.

A multivariate analysis of genetic and environmental influences on longitudinal height and weight data from a Swedish twin sample is presented. For height in boys, genetic correlations of all ages with the first time point decrease during puberty and increase afterwards. A more linear pattern is evident for the girls. For weight in boys, genetic and environmental correlations are similar to the ones for height. Genetic correlations for girls are stable with age, while environmental correlations peak at 13.5 years and decrease drastically thereafter. The patterns for height and weight in boys suggest that a new set of genes may be turned on during puberty and turned off again afterwards. The pattern found for weight in girls indicates that a simple additive genetic model is not appropriate. It is necessary, however, to apply the model to actual data from several time points to recognize the inadequacy of the model.

Self- and teacher-rated school adjustment in MZ and DZ twins.

In a Swedish longitudinal twin study, teacher ratings of school adjustment were collected in grades 3 and 6 for approximately 80 pairs of MZ twins, 100 pairs of DZ like-sex twins, and 70 pairs of opposite-sex twins. These same groups of twins then rated their own school adjustment in grades 4 and 6 as seen by the home, the school, their classmates, and themselves. A comparison of within-pair similarity for the different types of self-ratings tends to show more consistency and a higher concordance for MZ compared to DZ in grade 6 than in grade 4. The teacher ratings tend to show a larger and more consistent difference between MZ and DZ than the twins' own ratings. The results reported have certain implications for heritability estimates based on different types of ratings. Ratings by others thus seem to give the highest intraclass correlations, probably due to a certain halo effect. Self ratings, on the other hand, tend to fluctuate more over time at least for children before and at puberty. Also the construction of items seems to influence the magnitude of the correlations.

Intra-pair similarity in physical growth of opposite-sex twin pairs during puberty.

A comparison has been made of within-pair similarity in physical growth for opposite-sex twin pairs and pairs of unrelated controls attending the same classes as the twins. Height and weight measurements were originally collected for 97 pairs of twins and controls from 10 to 16 years of age for the girls and from 10 to 18 years for the boys. The twins showed significantly smaller within-pair differences than the controls for both height and weight during the whole investigation period. Within-pair correlations for height and weight were negative for the controls and moderately positive for the opposite-sex twins. The weight correlations for the twins were lower than for height from 11 to 14 years of age. At age 15 the height and weight correlations tended to be of the same magnitude due to a drop in within-pair similarity for height at this age. Profile similarity in physical growth has been studied both for each pair individually (D-values) and for the whole group of twins and controls (analysis of variance). Both comparisons showed both the twins and the controls to be very dissimilar in growth profiles during puberty. Onset of puberty was estimated by age at peak height velocity (PHV) and peak weight velocity (PWV). The average within-pair difference for the controls was shown to be a little more than two years and for the twins a little less. The small and non-significant differences between the groups lead to the main conclusion that sex differentiation at puberty exerts a very powerful influence overshadowing the hereditary and environmental similarities existing for the twins.

Intra-pair similarity in IQ of monozygotic and dizygotic male twins at 12 and 18 years of age.

Verbal and inductive test results have been collected for a group of male twins in grade 5 at 12 years of age and at enrollment to military service at 18 years of age. MZ twin pairs tend to get progressively more concordant for both verbal and inductive ability from age 12 to 18. DZ twins, on the other hand, get progressively more concordant for inductive ability, while they tend to get less concordant for verbal ability. The results are interpreted with reference to a model taking heredity-environment interaction into account. The discordant trend found when comparing intra-pair similarity in verbal ability for MZ and DZ twins thus seems to indicate the presence of interactional and correlational effects. For inductive ability, however, the difference between within-pair correlations for MZ and DZ twins tends to be of the same magnitude at both 12 and 18 years of age. Probably this type of test is less differentially influenced by the environments being sampled, at least under present circumstances, when children are not specifically trained to solve the kind of items included in the inductive test. Regression effects for the two tests and possible explanations to the increase from age 12 to 18 in both MZ and DZ within-pair similarity for inductive test scores are discussed.