A multi-center psychometric evaluation of the Severity Indices of Personality Problems 118 (SIPP-118): Do we really need all those facets?

PURPOSE: The Severity Indices of Personality Problems 118 (SIPP-118) is a self-report questionnaire that aims to measure core components of (mal)adaptive personality functioning that can change over time. In this study, we aimed to assess the facet strength of the 16 facets across three large clinical samples. METHODS: Data from Norwegian and Dutch psychiatric patients were analyzed in this international multi-center study (N(1) = 2814, N(2) = 4751, N(3) = 2217). Bi-factor modeling was used to assess to what degree the SIPP items tap into an overall general factor. The incremental value (distinctiveness) of the facets was studied using proportional reduction in mean squared error (PRMSE) based statistics. RESULTS: The estimated model showed adequate fit. The explained common variance (ECV) attributable to the general factor equaled 50% for all three samples. All but two facets (stable self-image and frustration tolerance) showed sufficient levels of distinctiveness. The findings were observed to be comparable across the three samples. CONCLUSION: Our findings showed that the general factor was relatively weak, and the facets had a clear incremental value.