Bouchard et al

Question 1

aim

Answer 1

to determine how much of intelligence can be attributed to genetics and how much to the environment

Question 2

procedure

Answer 2

Longitudinal study in 1979 and ongoing
Follows 100 sets of MZ and DZ twins and triplets raised both together and apart
It was cross cultural
The concordance rates between these twins could be compared to identical twins raised together and DZ twins raised together from around the world to explore the effects of nature vs nurture
Twins were given 50 hours of psychological and physiological testing
Including 4 personality tests
3 aptitude tests
2 intelligence tests
An IQ test

Question 3

results

Answer 3

Concordance rates for IQ were:
86% for MZ twins raised together
76% for MZ twins raised apart
55% for DZ twins raised together
Indicate that performance on IQ tests is highly heritable
They show a significant influence of environmental factors on IQ test scores

Question 4

conclusion

Answer 4

-Heritability of intelligence can be allocated 70% to genetics and 30% to other factors
-Intelligence is highly heritable

Question 5

strengths

Answer 5

As MZ twins share 100% of their genes, we can assume that any differences between them are due to the environment
Allows us to make reasonable and reliable conclusions about the effect of non-genetic factors
Example of a naturally occurring variable being changed for study. MZ twins share 100% of their genes and DZ twins share 50%
Researcher is not manipulating the variable himself so it reduces the risk of researcher bias

Question 6

limitations

Answer 6

concordance rates were high in the study but far from 100% s it was difficult to determine the relative influence of genes. Calculation of concordance rate is not always reliabel.
- there was no control for the effect of environmental variables in the study and this affects accurate estimations of genetic contribution to intelligence .
- twin study finding might not be generalizable to a wider population