Research studies of psychoanalytic psychotherapy have suffered from the absence of an operational definition of interpretation. The authors note that this term is

used to describe a variety of therapeutic behaviors. It may describe interventions to make unconscious mental processes conscious, or to enhance ego mastery of id, superego, and external reality. Some psychoanalysts differentiate interpretation from interventions such as clarification, translation, construction, and reconstruction; others use the term more globally to refer to all their interventions. The authors devised the Therapist Intervention Rating System (TIRS) to classify objectively the conduct of the psychotherapist. They propose ten general descriptive categories of intervention. These groupings seem adequate for classifying the different ways interpretations are made by psychotherapists who hold different theoretical positions. The TIRS does not, however, include criteria for rating the appropriateness of the content or the timing of the interventions.