Can somebody tell me where I can find the studies that say open adoption is best for the child?

Can somebody tell me where I can find the studies that say open adoption is best for the child?  My husband & I are adoptive parents who recently sought professional counsel as we were struggling with our birthfamily relationships.  The counsellor cited the ‘confusion theory’ and said we should close contact.  I would like to present the other side of the story but whenever I look for these studies about open adoption, all I find is one study done in the 90′s with 20 families.  Certainly there are more than that!