twin and adoption studies

• over how many years did Gottesman and shields (1966) study pairs of twins?

  16 years
• Gottesman and Shields (1966) studied pairs of twins where one had been diagnosed with schizophrenia
• Monozygotic twins happen when a single fertilized egg divides into two.
•  Dizygotic (fraternal) twins form when two separate eggs are released and fertilized by two sperm.
• Gottesman and Shields (1966) found that in MZ twins 42% of the co-twins also developed schizophrenia and in DZ twins 9% of co twins developed schizophrenia
• Gottesman and shields (1966) concluded that as concordance is higher in MZ twins than DZ twins, there could be a genetic basis for the development of schizophrenia
• how many pairs of MZ and DZ pairs of twins Coccaro et al (1997) use in their study?


  they studied 182 mz pairs and 118 dz pairs
• what gender of twins did Coccaro et al (1997) study?

  male
• Coccaro et al (1997) found that there was a high chance that aggressive traits would be found in both twins suggesting that impulsive aggression could be due to genetic factors
• what questionnaire did Coccaro et al (1997) use?

  the Buss-Durkee Hostility inventory which has 75 questions
• what does the Buss-Durkee Hostility Inventory test for?

  it assesses various emotional traits associated with aggression
• Coccaro et al (1997) compared the sores for each member of the twin pairs and found that a significant concordance rate was shown for measures such as indirect assault suggesting an element of heritability in some features of aggression
• Coccaro et al (1997) found that there was a high chance of aggressive traits being found in both twins suggesting that aggression could be partly due to genetic factor
• MZ twins share 100% genetics
• DZ twins share 50% genetics
• twin studies give psychologists a unique design to test the influence of nature/nurture on human behaviour
• adoption studies allow psychologists to measure if behaviour is a result of nature/nurture
• Cadoret and Stewart (1991) concluded that behaviour such as aggression has a variety of causes and is not significantly attributable to nature or nurture
• Cadoret and Stewart (1991) found that adopted boys were at an increased risk of ADHD and aggression as children if they had a biological parent who had been convicted of a crime in adulthood
• Cadoret and Stewart (1991) found that boys were more likely to be aggressive or have a diagnosis of ADHD if a member of the adopted family had psychiatric problems