The Strathclyde inventory as a measure of outcome in person-centred therapy

Student thesis: Doctoral Thesis


Person-centred therapy, like other humanistic therapies, proposes a potentiality model in which psychological growth, not simply the reduction of symptoms, is the anticipated outcome of therapy. Although substantial evidence of the effectiveness of person-centred therapy using medical model concepts exists, there is a need to develop measures that test outcome in therapy according to the person-centred theory of change. The Strathclyde Inventory (SI) is a brief self-report instrument designed to measure congruent functioning (described elsewhere as Rogers' fully functioning person, or congruence) for use as an outcome measure in therapy. The main purpose of this innovative three-part mixed method study was to investigate the validity of the SI as an outcome measure from multiple perspectives using data collected from a large UK-based clinical population. The first study evaluated the internal structure and reliability/precision of the instrument using the Rasch model. The second study investigated patterns of change in SI scores over the course of therapy seeking evidence of sensitivity to change, as well as convergent and construct validity. The third study tested the validity of change in SI scores as a measure of congruent functioning via a meta-synthesis of a series of eight systematic case studies examining client improvement and deterioration in therapy identified by pre-post change in SI scores. The results supported the validity of the SI as an internally consistent and precise unidimensional instrument that is able to identify meaningful change in congruent functioning within a UK-based clinical population. A brief 12-item version of the instrument was produced. An evidence-based, theoretically coherent, developmental pathway for congruent functioning was proposed, identifying self-acceptance as a pivot point. Overall, the results of this three-part study established that change in participants' scores during therapy demonstrated a high degree of variation and proposed an explanation for different post-therapy outcomes in congruent functioning.
Date of Award30 Apr 2020
Original languageEnglish
Awarding Institution
  • University Of Strathclyde
SupervisorRobert Elliott (Supervisor) & Diane Dixon (Supervisor)

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