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The Outcome Questionnaire-45 (OQ-45) is a 45-item instrument designed to be used by psychotherapists to track their clients' distress over time. The OQ-45 is composed of three factors: symptomatic distress, interpersonal relations, and social role performance. Numerous researchers have attempted to replicate this intended three-factor structure in their own data, only to find poor fit. Attempts to find a factor structure that does show adequate fit have been met with mixed, but generally poor, results. Additionally, very little work has been done to establish that the OQ-45 exhibits sufficient longitudinal measurement invariance to allow comparison of OQ-45 scores over time. Notwithstanding these known issues regarding the fit of the OQ-45, it has been adopted widely in many countries and translated into several dozen languages. This study sought to identify a factor structure of the OQ-45 that did exhibit longitudinal measurement invariance. Using a sample of 7,751 clients who made 56,353 visits to Brigham Young University's Counseling and Psychological Services between 1996 and 2017, three factor structures were analyzed using Mplus 8.2 through confirmatory factor analysis: (a) single-factor, (b) intended three-factor, and (c) bifactor models. The bifactor model fit the data best, as determined by standard fit statistics (CFI, TLI, RMSEA, SRMR). However, this bifactor model still had inadequate fit. At this point, exploratory structural equation modeling (ESEM) using target rotation was applied to the bifactor model. This ESEM bifactor model had a dominant general factor and did have good fit to the data. Having selected the ESEM bifactor model, it was then tested to see if it showed longitudinal measurement invariance over five time points (the initial OQ-45 score at the intake appointment, followed by four subsequent appointments). The OQ-45 items were treated as categorical and analyzed using the WLSMV estimator. Four time sequences were examined for configural, metric, and scalar longitudinal invariance: Time 1 to Time 2, Time 1 to Time 3 (inclusive of Time 2), Time 1 to Time 4 (inclusive of Times 2 and 3), and Time 1 to Time 5 (inclusive of Times 2, 3, and 4). The OQ-45, when modeled as an ESEM bifactor model, does exhibit scalar longitudinal measurement invariance. Using a new method developed by Clark (2020), ΔSRMR between adjacent models (configural to metric, metric to scalar) were all below his recommended guideline of .01. This is the first study to find a good fitting model of the OQ- 45 that can be used to assess changes in clients' psychological functioning over time. Total OQ- 45 scores can continue to be used by therapists to monitor their patients with confidence in its longitudinal psychometric properties.

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

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The Yale-Brown Obsessive-Compulsive Scale (Y-BOCS) is considered the “gold standard” for measuring symptoms for Obsessive-Compulsive Disorder (OCD) due to the high reliability and validity of the measure. Originally, the Y-BOCS was divided into Obsessive and Compulsive factors; however, literature on the factor structure of the Y-BOCS is inconsistent. Models range from one global factor to different interpretations of bi-factor models to three-factor models. Inconsistencies between models may be attributed to sampling error, including participants with subclinical OCD in some samples, and measurement error. In addition, many researchers treat the Y-BOCS measurement as an interval or ratio scale when it likely reflects ordinal measurement. Our paper has two primary aims. First, we compare the fit of the models proposed in the literature using a large sample from multiple sites of patients diagnosed with OCD. We also evaluate how the models can be improved and whether those improvements show evidence for convergent validity. We treat the Y-BOCS observations as ordinal data. Second, we evaluate measurement and structural invariance between genders. Additionally, we examine convergent validity of the factor structure of the best fitting model with subscales of the OCI-R. Data from five separate samples were combined into one dataset with 288 total participants all formally diagnosed with OCD. We selected several Y-BOCS factor models from the literature and used confirmatory factor analysis to evaluate goodness of fit indices on our pooled sample. Only one model approached acceptable goodness of fit indices. We considered the factors in this model and proposed a new factor model with a global factor (OCD) and two sub-factors (Obsessions and Resistance to Symptoms). Our model exhibited the highest goodness of fit indices which we further improved with modifications to our factor model. On invariance analyses, our model exhibited measurement invariance between genders and partial structural invariance. Additionally, the latent factors of our model exhibited convergent validity with all of the OCI-R subscales (except Ordering). Our model exhibited stronger goodness of fit indices with our data than existing models in the Y-BOCS literature and measurement invariance and partial structural invariance between genders. We recommend that future studies replicate the efficacy of our factor model using the Y-BOCS as an ordinal measurement.

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