Interpreting the Inventory of Interpersonal Problems: subscales based on an interpersonal theory model.

There remains considerable debate about a theoretically interpretable subscale structure for the Inventory of Interpersonal Problems (IIP). In this paper items are extracted from the IIP to form a 40-item shortened version (the IIP-40) comprising eight subscales, each of five items, which conform to the eight octant positions within Birtchnell's interpersonal octagon: a version of interpersonal theory. The inter-item reliability of the subscale structure is found to be acceptable when tested against a sample of 150 pre-assessment for psychotherapy IIP completions within the Centre for the Study of Psychotherapy (CSP), University of Kent. The face validity is established through acceptable inter-rater reliability scores in an experiment using blind raters. Subscale scores are shown for patients within CSP and are found to be significantly different between genders in the octant positions of Upper Close and Neutral Distant. High scores in the octant position of Upper Distant is found to be a significant predictor of therapeutic drop-out. The results for gender and therapeutic engagement are consistent with other published work in the interpersonal theory field.