Zirogiannis (2001) states that there is no universally recognized standard for assessing the reliability and validity of expert social science evidence. Nevertheless, three American cases are frequently referred to in the literature concerning parental alienation syndrome: Frye v. United States, Daubert v. Merrill Pharmaceuticals, and Kumho Tire v. Carmichael. In Frye v. United States, scientific evidence was considered admissible if it was based on generally accepted professional standards. This has come to be referred to as the general-acceptance standard for evidence. Subsequently, in Daubert v. Merrill Pharmaceuticals, the judges were viewed as having gatekeeping responsibilities with respect to the admissibility of evidence based on a four-step test. Non-binding considerations for judges were suggested in this Daubert decision. This is referred to as the multiple-factor test. The United States Supreme Court addressed questions related to expert evidence in Kumho Tire v. Carmichael. The Court concluded that judges have considerable discretion to determine reliability and validity. Zirogiannis states that this decision permits the introduction of novel expert analysis. Refer to Zirogiannis (2001) for a more detailed explanation of evidentiary issues for the introduction of expert evidence.