background and aim- what psycholgists mean by intelligence and biological factors that could affect it. ravens progressive matrices test. aim was to investigate identical twins and non identical twins and other siblings as well as parents
method- series of mini case studies and the use of self reports. correlational study
sample- 112 families from the Netherlands (access by twin registry from the vu uni of amsterdam) contacted via letter. 23 pairs of male monozygotic twins. 23 pairs of male dizygotic twins. 25 pairs female mz twins =. 21 pairs female dx twins. 20 pairs of dz opposite sex twins
procedure- completed a questionaire and DNA test to see if MZ or DZ. children completed Ravens standard progressive matrices (60 problems divided in to 5 sets of 12) in separate rooms and adults completed the advanced one.
results- higher correlations for MZ twins than first degree relatives. variance for siblings was larger tha for twins. moderate correlation for spousal IQ. genetics accounts for 67% of variation in intelligence and the remainder is due to environmental factors
conclusions- variability in fluid intelligence is largely explained by genetic effects that are passed from parents to children. individual differences in intelligence are largely accounted for by genetic differences
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