- AO1- Robertson and Robertson, case studies, residential nursery, hospital and in their care. Some underwent PDD.
- AO2- Skodak and Skeels IQ levels in orphanage and a home for the mentally retarded.
- AO2-Bifulco- 249 women whos mothers had died before they were age 17. 50% more likely to develop depression
- AO2- Bohman and Sigvardson, 600 adopted children 26% 'problem children' 10 years later they were normal