Psychometric validation of the obsessive belief questionnaire and interpretation of intrusions inventory—Part 2: Factor analyses and testing of a brief version
Introduction
Recent theoretical and empirical work suggests that several cognitive constructs (e.g., inflated responsibility, overestimation of threat, thought-action fusion, intolerance of uncertainty) are relevant to the development and exacerbation of obsessive-compulsive (OC) symptoms (Freeston, Rheaume, & Ladouceur, 1996; Frost & Steketee, 2002; Purdon, 2001). Cognitive strategies for treating obsessive-compulsive disorder (OCD) have been based on the modification of key beliefs and appraisals formulated in these theories (Rachman, 1998; Salkovskis & Warwick, 1985; van Oppen & Emmelkamp, 2000; Whittal & McLean, 1999). Clearly, it is important to measure cognitive constructs hypothesized to be relevant to OCD. Many such measures have been developed in recent years, but with little consensus regarding which domains to assess and very limited psychometric information regarding these scales (Taylor, Kyrios, Thordarson, Steketee, & Frost, 2002).
To address these concerns a large group of international researchers, the Obsessive Compulsive Cognitions Working Group (Obsessive Compulsive Cognitions Working Group (1997), Obsessive Compulsive Cognitions Working Group (2001)), identified domains considered central to OCD and developed the 87-item Obsessive Beliefs Questionnaire (OBQ) and the 31-item Interpretation of Intrusions Inventory (III). Six rationally derived subscales of the OBQ-87 (overestimation of threat, intolerance of uncertainty, importance of thoughts, control of thoughts, responsibility, and perfectionism) and the three subscales of the III-31 (control of thoughts, importance of thoughts, responsibility) showed good internal consistency but were highly intercorrelated. Findings from initial testing provided preliminary evidence for the reliability and validity of these instruments, but further study of reliability and specificity of the measures using larger samples was needed.
Part 1 of this investigation (OCCWG, 2003) described the reliability and convergent and discriminant validity of the original, rationally derived subscales of the OBQ and III using four samples who completed the English language version of the instruments. These included 248 participants with OCD as their primary (most severe) disorder (OC), 105 anxious controls (AC), 87 community controls (CC) and 291 student controls (SC). Results indicated that the belief and appraisal dimensions represented by the OBQ and III subscales showed good internal consistency and good test–retest reliability over a 2–3 month interval. Findings for criterion-related (known-groups) validity based upon comparisons of four subject samples were generally good. The OCs scored significantly higher than both non-clinical samples (SC and CC) on every subscale, and scored higher than ACs on 3 (Responsibility, Control, and Importance of thoughts) of the 6 OBQ subscales and 2 (Responsibility, Control of thoughts) of the 3 III subscales. Thus, beliefs related to Tolerance for Uncertainty, Overestimation of Threat, and Perfectionism and appraisals related to Importance of Thoughts appeared to be relevant but not specific to OCD.
As evident from their moderately high intercorrelations, the subscales of the OBQ and subscales of the III overlapped, suggesting that the appraisal and belief domains measured by these scales may not be well differentiated from one another. Convergent validity was evident in the moderate correlations of almost all OBQ subscales, except Importance of Thoughts with measures of OC symptoms, but the III showed a more variable pattern of association. With respect to discriminant validity, correlations of the cognitive measures with measures of non-OC symptoms (e.g., depression and general anxiety) was approximately as high as those with OC symptoms. This lack of specificity was apparent in both OC and non-OC samples. To further clarify discriminant validity, a series of analyses were conducted to partial out the influence of other measures. The OBQ and III showed a specific relationship with OC symptoms even after controlling for worry, but both instruments appeared to have relevance for other negative affective states, such as worry, and may not be unique to OCD.
The aim of the present paper is to report on a factor analysis of the OBQ and III using a large sample of OCD participants to determine whether a reduced item pool would be more efficient in capturing the beliefs underlying OCD. This study also explores whether a smaller number of dimensions are relevant for assessing the beliefs, interpretations and other cognitive constructs associated with OC symptoms. The psychometric properties of empirically based, rather than theoretically derived, subscales are examined using the multi-site data set described in the Part 1 paper that includes non-OCD clinical and non-clinical samples.
Section snippets
Method
The methodology employed for this paper is summarized below. A complete description is available elsewhere (OCCWG, 2003).
Factor analyses
Given the elevated inter-correlations among the rationally derived subscales of the OBQ and III, we sought to determine whether more distinct empirically derived dimensions might underlie the OBQ and III. A priori, it was unclear how the scales might be combined into a parsimonious set of underlying dimensions. The high subscale intercorrelations indicated that it was unlikely that each subscale would correspond to a distinct factor. In the absence of alternative, previously defined factor
Discussion
The present study sought to determine whether factor analyses of the 87-item OBQ and 31-item III would permit reduction of the number of items, particularly for the OBQ which is quite lengthy for use in clinical settings. We also sought to reduce overlap among factors evident in high correlations among subscales in our previous study (OCCWG, 2003). Three factors emerged for the OBQ, and inclusion of high loading items yielded a 44-item total scale with three subscales of approximately similar
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Co-Chairs: Gail Steketee and Randy Frost. The members of the working group who contributed to this study are (in alphabetical order): Sunil Bhar, Martine Bouvard, John Calamari, Cheryl Carmin, David A. Clark, Jean Cottraux, Paul Emmelkamp, Elizabeth Forrester, Mark Freeston, Randy Frost, Celia Hordern, Amy Janeck, Michael Kyrios, Dean McKay, Fugen Neziroglu, Caterina Novara, Gilbert Pinard, C. Alec Pollard, Christine Purdon, Josee Rheaume, John Riskind, Paul Salkovskis, Ezio Sanavio, Roz Shafran, Claudio Sica, Gregoris Simos, Ingrid Sochting, Debbie Sookman, Gail Steketee, Steven Taylor, Dana Thordarson, Patricia van Oppen, Ricks Warren, Maureen Whittal, Sabine Wilhelm, and Jose Yaryura-Tobias. Special thanks to Michael Kyrios, Steve Taylor, and Dana Thordarson for conducting data analyses, to Cheryl Carmin for drafting the manuscript, and to Neil Rector for contributing additional data to the project.