Humphreys KL, McLaughlin KA, Sheridan MA et al. J Clin Psychol Psychiatry. 59(7): 811-821. https://doi.org/10.1111/jcpp.12865

 This 10 year follow-up study of children who had experienced severe early deprivation by 22 months found that by 12 years of age, 40% exhibited adaptive functioning, with a greater proportion (56%) doing so if they had received foster care than if they had received care as usual (23%). Foster placement before 20 months of age resulted in greater likelihood of achieving the threshold for adaptive functioning (79%) than foster placement after 20 months (46%).

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