Psychometric arguments for the use of non-ipsatized scores in the Inventory of Interpersonal Problems (IIP-D)

Background: In the manual of the Inventory of Interpersonal Problems (IPP-D), the use of ipsatized scores is suggested in order to eliminate the influence of a potentially interfering factor. Objective: Should these suggestions be followed or would non-ipsatized scale scores be the better option? Method: 129 adults completed the IIP-D as well as the Trier Integrated Personality Inventory (TIPI). Factor analyses were carried out, and reliabilities and validities of the non-ipsatized and ipsatized IIP-D scale scores were compared. Results: Compared to the non-ipsatized scores, internal consistencies based on the ipsatized scores were clearly lower. Furthermore, a factor analysis of the non-ipsatized scores indicated that the putative interfering factor is actually a general measure for the degree of interpersonal problems, correlating highly with Neuroticism and significantly with Introversion and Disagreeableness. Two further factors represent a rotated version of the circumplex model of interpersonal behavior. Conclusions: The psychometrical findings as well as a clinical case study strongly suggest the use of non-ipsatized scores.