The Strathclyde Inventory-Revised (SI-R): Developing an outcome measure based on Rogers' theory of therapeutic change

Results from comparative outcome studies suggest the general equivalence of psychotherapeutic treatments based on different theories and techniques, leading some to the Dodo bird verdict that “everybody has won so all shall have prizes”. However, it can also be argued that different outcomes do occur but are not detected by current research strategies. It is important, therefore, to develop research methods which have the potential to assess humanistic therapy's specific effects.

This paper reports on the refinement of such an outcome measure, the Strathclyde Inventory. The original measure was developed in 2006 according to Rogers' description of the 'fully functioning person', encompassing the dimensions of locus of evaluation, open-ness to experience, self-liking, existential living, acceptance of others and psychological adjustment. Using several sets of clinical and nonclinical data, the instrument has undergone additional analysis and item reduction using item response theory (Rasch analysis). This streamlined version manifests a bi-dimensional structure of congruence / incongruence which is seen to reflect Rogers’ core hypothesis of client distress. Further, we have been able to establish reliable change values and refined cut-off values for distinguishing between clinical and nonclinical levels of distress (overall mean = 2.46). This makes it possible to use the SI-R to assess reliable and clinically significant change.