Who? Nestadt et al. - 68% of monozygotic twins shared OCD compared to 31% of dizygotic twins + family studies showed a person with a family member with OCD is four times as likely to develop it
Why? Some genetic influence
Limitation: Environmental risk factors
What? Environmental risk factors
Who? Cromer et al. - over half of clients had experienced a traumatic event in their past
Why? Genetic vulnerability only a partial explanation
