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Limitation of twin studies is assuming equal environments
Often assumed that environmental factors are the same for MZ and DZ twins because they experience similar environments
However because MZ twins look identical people tend to treat them more similarly which in tern their behaviour
Therefore, higher concordance rates on MZ Maybe because they are treated more similarly than DZ suggesting conclusions lack validity
Strength is that it supports the diathesis-stress model of offending
Mednick et al studied 13,000 Danish adoptee having at least one court conviction.
Conviction rates
13.5% biological or adoptive parents had no convictions
20% one biological parent
24.5 both adoptive and biological parents
This data suggests that both genetic inheritance environment influences criminality Supporting the diathesis stress model of crime
Nature and nurture
Adoption study separate nature and nurture similarities due to biological parent can only be genetic
However many adoptions occur when children are older and adoptive maintain contact with biological family so still environmental influence
This suggests that adoption studies cannot fully separate Nature and nurture
Summary of the evaluation
Strength supports diathesis stress model
Limitation assumes equal environments of twins as monozygotic twins get treated the same which in tern affects behaviour and this lacks
Many adult days still maintain contact with biological family and adopted when they’re older so adoption studies cannot fully separate nature and nature