The evidences of the effectiveness of any psychological intervention requires the demonstration of its internal and external validity, what is usually made by inferential statistical methods. An alternative, more recently explored, especially in the realm of the psychotherapeutic processes, is based on indexes of reliability and clinical significance of the changes. Among the methods used to produce these indexes, it is highlighted that one developed by Jacobson and Truax (1991), known as "JT Method", still rare in the Brazilian psychological research. This study briefly presents the rational and some methodological and practical issues concerned with this method, exemplifying its use in the data analysis of a fictitious intervention.
JT Method; internal validity; external validity; psychotherapy; psychoeducational intervention
