The appearance of multidimensionality: Exploring the case for unidimensionality of the PTSD Checklist for DSM-5 using a firefighter sample.

Rasmussen et al. (2019) described the proliferation of factors for posttraumatic stress disorder (PTSD) measures and raised concerns about the construct validity of factors that include two or three items. In this brief report, we describe how the pattern of covariation among the responses to items of well-established measures, such as the PTSD Checklist for DSM-5 (PCL-5), can give the appearance of multidimensionality. We evaluated whether the structure of the 20-item PCL-5 is unidimensional, using the methods of multidimensional item response theory (MIRT) and the concept of a testlet. These analyses were done using a sample of trauma-exposed urban firefighters. A unidimensional and a bifactor model, which includes a general factor composed of all items and four specific factors mirroring the DSM-5 conceptualization, were evaluated for both Likert-type multiple-category and binary coding system of the PCL-5 item response data. Seven testlets were created from the 20 PCL-5 items following the seven-factor model (Armour et al., 2015) presented in Table 1 of Rasmussen et al. (2019). Findings using the unidimensional nominal item response theory model for the seven testlets indicated that the PCL-5 may be considered unidimensional with a single score representing individual differences on a continuum that ranges from low to high. (PsycInfo Database Record (c) 2024 APA, all rights reserved).