The adoptee population does, however, seem to be more at risk for certain behavioral issues. Researchers from the University of Minnesota studied adolescents who had been adopted and found that adoptees were twice as likely as non-adopted people to suffer from oppositional defiant disorder and attention-deficit/hyperactivity disorder (with an 8% rate in the general population).[135] Suicide risks were also significantly greater than the general population. Swedish researchers found both international and domestic adoptees undertook suicide at much higher rates than non-adopted peers; with international adoptees and female international adoptees, in particular, at highest risk.[136]
United States approx 136,000 (2008)[69] 3,978,500 (2015)[70] ≈3 per 100 live births The number of adoptions is reported to be constant since 1987. Since 2000, adoption by type has generally been approximately 15% international adoptions, 40% from government agencies responsible for child welfare, and 45% other, such as voluntary adoptions through private adoption agencies or by stepparents and other family members.[69]
Embryo adoption: based on the donation of embryos remaining after one couple's in vitro fertilization treatments have been completed; embryos are given to another individual or couple, followed by the placement of those embryos into the recipient woman's uterus, to facilitate pregnancy and childbirth. In the United States, embryo adoption is governed by property law rather than by the court systems, in contrast to traditional adoption.
Other studies provide evidence that adoptive relationships can form along other lines. A study evaluating the level of parental investment indicates strength in adoptive families, suggesting that parents who adopt invest more time in their children than other parents and concludes, "...adoptive parents enrich their children's lives to compensate for the lack of biological ties and the extra challenges of adoption."[94] Another recent study found that adoptive families invested more heavily in their adopted children, for example, by providing further education and financial support. Noting that adoptees seemed to be more likely to experience problems such as drug addiction, the study speculated that adoptive parents might invest more in adoptees not because they favor them, but because they are more likely than genetic children to need the help.[95]
His solution was outlined in The Best Method of Disposing of Our Pauper and Vagrant Children (1859) which started the Orphan Train movement. The orphan trains eventually shipped an estimated 200,000 children from the urban centers of the East to the nation's rural regions.[28] The children were generally indentured, rather than adopted, to families who took them in.[29] As in times past, some children were raised as members of the family while others were used as farm laborers and household servants.[30] The sheer size of the displacement—the largest migration of children in history—and the degree of exploitation that occurred, gave rise to new agencies and a series of laws that promoted adoption arrangements rather than indenture. The hallmark of the period is Minnesota's adoption law of 1917 which mandated investigation of all placements and limited record access to those involved in the adoption.[31][32] 
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