The Strathclyde Inventory: Measuring congruence as an outcome of therapy

Activity: Talk or presentation typesOral presentation


Aim/Purpose: Levitt et al (2005) challenged researchers to develop outcome measures that test the potentiality model underpinning humanistic therapies. Freire, Elliott & Cooper, (2007) responded by developing the Strathclyde Inventory (SI), an outcome measure consistent with person-centred theory of psychological growth (i.e. congruence-incongruence). The purpose of this study was to conduct a robust investigation of the reliability and validity of the SI using data collected from a large clinical population.

Design/Methodology: Rasch measurement (Bond & Fox, 2015) aims to develop genuine interval (“ruler-type”) measures based on a model that orders persons according to ability and items according to difficulty. In this study the Rasch model was applied to assess the SI’s rating scale design and developmental pathway (item-person fit and separation) using data collected at the Strathclyde Research Clinic from 406 clients who accessed person-centred therapy and completed the SI at one or more points during their therapeutic process (total N=1174). These analyses used a brief 16-item version of the SI developed in 2012.

Results/Findings: Analyses revealed a well-functioning 5-point rating scale, with clients able to discriminate between all rating scale points. The standardised fit statistics (infit, outfit and root mean square error) demonstrated a strong fit between the Rasch model and the persons and items measured by the SI. Separation indices identified at least three distinct sub-populations of persons and 11 item separations indicating that the SI is capable of measuring distinctive groups of individuals within an ordered set of items that represent graded levels of congruence, ranging from making choices based on internal locus of evaluation to living fully in the moment.

Research Limitations: Rasch analysis is a powerful tool but may risk over-simplifying a complex phenomenon such as congruence by treating it as a single dimension. In this study, the use of multiple observations from the same clients can also be criticised for statistical assumptions.

Conclusions/Implications (including practice implications): This study provides strong evidence that the SI is capable of genuine interval measurement of congruence within a clinical population. We encourage therapists to introduce the SI within their practice as an outcome measure consistent with person-centred theory of psychological growth.

Period19 May 2017
Event title23rd Annual BACP Research Conference: Research and reflective practice for the counselling professions
Event typeConference
LocationChesterShow on map
Degree of RecognitionNational


  • Measurement
  • Rasch Analysis
  • outcome research
  • person-centred
  • Strathclyde Inventory