4
information about the school entrants, the teachers grounded their assessments on the cognitive,
verbal and social competencies of the children, as an informal inquiry showed. The children
were assigned for each of the social classes to either high competence" or "low competence".
The teachers' judgments can be considered as a global rating of the subjects' competence level
at the onset of the longitudinal study, which was cross-validated with the cognitive and socio-
cognitive data of Wave 1. The predictive power of the teacher rating proved considerable. The
regression on a summary measure of cognitive competence about six month later produced a
correlation coefficient ofr=.74.
The competence level' was introduced to contrast differential impacts of this variable on the
individual trajectories of the children and - supposing decelerated developmental speed within
the lower competence' sample - to focus developmental processes with a finer grade.
Social class
To determine the social class of the parents the status measures of Björnsson, Edelstein &
Kreppner (1977, S. 29ff.) were used. Six classes were distinguished, whose relative
proportions of the Icelandic population are shown in brackets:
1)
Unskilled workers (26,1%);
Skilled workers and craftsmen (31,3%);
2)
unskilled and skilled clerical workers and civil servants (10,0%);
4)
technical or teaching professions, lower managerial (14,8%);
5)
employers, businessmen or higher managerial professions (9,9%);
6)
academic professions including secondary teachers, artists and leading occupations in
the political or administrative system (7,8%).
Attrition rate: Despite the wide long time range of the study (8 years from the first to the fisth
wave) the drop out rate is rather small; it amounts to less than 10 % for the urban and less than
5% for the rural sample.
Population percentages from census data in the Handbook of statistics of Iceland.