Twin Study

• Twin Studies:

  Strengths:

  • Because monozygotic twins are genetically identical, it is logical to examine whether their offending behaviour is also identical
  • Twin studies give some support to genetic explanations. Ishikawa and Raine found a higher concordance rate for identical than non-identical twins. The concordance rate measures the probability of both twins being criminals if one of them is
• Twin Studies:

  Limitations:

  • If genes were the only cause of criminality, identical twins would show 100% concordance, but studies only show about half or less.
  • Higher concordance rates between identical twins may be due to the same home, school etc. Their shared environment might cause similarities in their criminal behaviour, not identical genes.
• Twin Studies:

  Limitations (2):

  • Parents treat identical twins more alike than they do non-identical twins. Also, identical twins may feel closer than non-identical twins, so one twin may be influenced but the others criminality to become criminal too. These environmental factors may produce similarities in behaviour
  • It’s impossible to isolate and measure the effect of genes separately from environmental effects.
  • In early studies, there was no way of knowing for certain if twins were in fact genetically identical, since DNA testing did not exist.