adoption study - tienari

• Adoption studies


  Compare the concordance rate of an adoptee with their biological and adoptive parents
• If children are more similar to their biological parents with whom they share genes but not environment, than to their adoptive parents with whom they share environment but not genes


  Then a trait/behaviour is a result of genetic factors
• Shared Genes


  • Biological Parents
  • Adopted Child
• Shared Environment


  • Adoptin Parents
• Tienari (2004)


  Adopted children from families with schizophrenia (SZ) were compared to adopted children from families without SZ
• Those with family history of SZ had more chance of developing the illness (9.4% lifetime risk) than children from families with no history of SZ (1.2% lifetime risk)
• This supports a genetic link
• However, those children from families with SZ were less likely to develop the illness if placed in a "good" family with kind relationships, empathy, security, etc
• So environment does play a part in triggering the illness
• Strengths of adoption studies

  • Adoption studies control the influence of environment so differences between sets of adoptees can be said to be genetic
  • Tienari found adoptees whose mother's had SZ had a higher lifetime risk of developing SZ (9.4%) than compared to adoptees whose mothers did not have SZ (1.2%). Therefore the influence of nature vs nurture can be measured
• Weaknesses of adoption studies

  • Adoptive studies may lack validity because of selective placement
  • The adoptive children in Tienari's study may have adoptive families similar to their biological ones. Therefore some of the similarities with biological relatives is actually due to environmental similarities rather than genes
  • Adoption studies have limited generalisability
  • Parents in Tienari's study were likely to be better educated, low rates of mental health issues and have high income. Therefore conclusions about the effects of genes on SZ may not be generalisable to the population as a whole
• Useful to show the environment may play a greater role than twin studies suggest