Though not the first methodology in the practice of individual verbal psychotherapy, Freud's psychoanalytic system came to dominate the field from early in the twentieth century, forming the basis for many later variants. While these systems have adopted different theories and techniques, all have followed Freud by attempting to achieve psychic and behavioral change through having patients talk about their difficulties. Psychoanalysis is not as influential as it once was in Europe and the United States, though in some parts of the world, notably Latin America, its influence in the later 20th century expanded substantially. Psychoanalysis also remains influential within many contemporary schools of psychotherapy and has led to innovative therapeutic work in schools and with families and groups. There is a substantial body of research which demonstrates the efficacy of the clinical methods of psychoanalysis and of related psychodynamic therapies in treating a wide range of psychological disorders.