The Hague Convention seeks to avoid this, also in the United States of America, the Uniform Child Custody Jurisdiction and Enforcement Act was adopted by all 50 states, family law courts were forced to defer jurisdiction to the home state. In the context of cases regarding custody, the "best interest" rule suggests that all legal decisions made to accommodate the child are made with the goal of ensuring a child's happiness, security and overall well being. There are many different factors that go into the decision that is made in a child's best interest, which include: the child's health, environment and social interests, the relationship each parent has with the child, and the ability of each parent to address the needs of the child. The "best interest" rule has been considered to be a standard in determining child custody for the most recent 40 years in history. Although it has been so widely favored amongst legal systems, there are some deficiencies to the concept. Robert Mnookin, an American lawyer, author, and a Professor of Law at Harvard Law School, claimed that the best interest rule is indeterminate. It is considered to be a broad and vague set of guidelines that only leads to increased conflict amongst the parents instead of promoting cooperation that would actually lead to the best interest of the child being met. Some of these problems specifically include: In order to better analyze the "best interest" of children, several experiments were conducted to observe the opinions of children themselves. Children of divorce were found to want equal time with both of their parents. Studies conducted by Wallerstein, Lewis and Blakeslee (2002) show that children from all age ranges indicate that equal or shared parenting is of their best interest 93 percent of the time. Several other studies were able to produce similar results, including Smart (2002), Fabricus and Hall (2003), Parkinson, and Cashmore and Single (2003). As a result, there has been a push to allow for joint custody of children in the most recent years, which strives to best meet the interests of the children and most evidently favors a gender neutral stance on the custody issue. However, the decision is highly situational, for joint custody can only be achieved in the absence of certain exceptions. For example, history of domestic violence found from either parent can most certainly trump the possibility of joint custody for a child. In an economic analysis, Imran Rasul has concluded that if one parent values child quality more than the other, the spouses prefer that parent to have sole custody, while joint custody is optimal for parents with relatively equal valuation of child quality.