Bouchard et al (1990)

Aim

Aim

to investigate the extent to which genetic inheritance affects intelligence

Method

Concordance rates for variables including IQ were found for a self-selected sample of MZ (identical) twins. The participants were separated into twins raised together (MZT) and apart (MZA).

Results

It was found that the concordance rate for IQ, as measured through the standardized intelligence test WAIS, was 69% for MZA and 88% for MZT.

Conclusion

IQ is, to a large extent, inherited, as well as being affected by environmental factors. They also proposed that 70% of observed variation in the sample could be a result of genetic variation.

Strengths

1. The study's longitudinal design allowed for the investigation of genetic and environmental influences on traits over an extended period

2. Utilizing MZ and DZ twins enabled the exploration of genetic and environmental contributions to various characteristics

3. Bouchard's study employed rigorous measures and methodologies, enhancing the reliability and validity of the findings

Weaknesses

1. Findings may not be easily generalizable beyond twins or to the broader population due to the unique characteristics of the sample

2. The study may not definitively prove that genetics or the environment directly cause certain traits because traits are influenced by a complex mix of genetic and environmental factors that interact in intricate ways

3. Ethical Concerns

Ethical Considerations

1. Reuniting separated twins raises questions about implications and stress, but most are eager to meet, according to Bouchard

2. Twin studies rely on identifying and recruiting willing participants from adoption records

3. Participation is voluntary with awareness that anonymity may not be fully maintained

4. Confidentiality is preserved as names are not revealed in research publications

5. Informed consent issues when twins are identified through adoption records, making it hard for participants to decline participation upon discovering a long-lost twin