Dysfunctional beliefs in the understanding & treatment of obsessive compulsive disorder Polman, Annemieke

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1 University of Groningen Dysfunctional beliefs in the understanding & treatment of obsessive compulsive disorder Polman, Annemieke IMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite from it. Please check the document version below. Document Version Publisher's PDF, also known as Version of record Publication date: 2010 Link to publication in University of Groningen/UMCG research database Citation for published version (APA): Polman, A. (2010). Dysfunctional beliefs in the understanding & treatment of obsessive compulsive disorder. Groningen: s.n. Copyright Other than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons). Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Downloaded from the University of Groningen/UMCG research database (Pure): For technical reasons the number of authors shown on this cover page is limited to 10 maximum. Download date:

2 Obsessive beliefs and their relationship to obsessive-compulsive symptom dimensions Submitted for publication as: Polman, A., Bouman, T.K., Huisman, M., De Jong, P.J. & Den Boer (2010). J.A. Obsessive beliefs and their relationship to obsessive-compulsive symptom dimensions.

3 Abstract Obsessive-compulsive disorder is a heterogeneous condition characterized by diverse symptom patterns. Moreover, treatment response is variable. Therefore, identification of OCD subtypes might contribute to our understanding of OCD, and may advance aetiologic theory. Considering the emphasis on dysfunctional beliefs in contemporary theories of OCD, the current study investigated the relationship between dysfunctional beliefs and OC symptom dimensions, in order to further the characterization of OCD subtypes. One hundred and twentytwo patients with OCD according to DSM- IV-TR completed questionnaires concerning OC symptoms and beliefs. Furthermore, OC symptoms were assessed with a semi structured interview. Multiple regression analyses showed specific relationships between belief domains and symptom subtypes; Importance and Control of Thoughts was associated with Impulses, Responsibility and Threat Estimation was related to Rumination, and beliefs related to Perfectionism and Certainty were associated with Checking, Rumination, and Precision. No relationship was found between beliefs and washing symptoms. These results suggest that dysfunctional beliefs are related to several OC symptom dimensions and could contribute to a more sophisticated characterization of OCD subtypes.

4 OBSESSIVE BELIEFS AND OCD SYMPTOM DIMENSIONS 63 Introduction Obsessive-compulsive disorder (OCD) is a heterogeneous disorder, and its symptom presentation can take many forms (e.g., washing, checking, hoarding, and harming obsessions). This diversity in symptoms, along with differences in treatment response and neurobiological differences, have led researchers and clinicians to propose that important subtypes of OCD exist (cf. McKay, Abramowitz, Calamari, Kyrios, Radomsky, Sookman, et al., 2004). Research to identify these subtypes mainly focused on symptom presentation. This led to the following replicable symptom subtypes: contamination and washing/cleaning, harm obsessions and checking rituals, obsessions without overt compulsions, and hoarding (McKay et al., 2004). Besides differential treatment response, symptom subtypes also show information processing differences. For instance, checkers are characterized by slowness and indecisiveness (Rachman, 2002), and tend to have less confidence in their memory (Radomsky, Rachman & Hammond, 2001), whereas the hoarding subtype shows organization and categorization deficits (Frost & Hartl, 1996). Contemporary theories emphasize the mediating role of dysfunctional beliefs in the development and maintenance of OCD (Frost & Steketee, 2002; Salkovskis, 1985), and further characterization of subtypes could benefit from studying the association between dysfunctional beliefs and symptom subtypes. Accordingly, exploratory research revealed that, for example, thought-action fusion was related to washing and checking, whereas probability of risk/harm was associated with washing, checking, and precision (Emmelkamp & Aardema, 1999). An international group of researchers identified six important theoretical belief domains; overimportance of thoughts, importance of controlling one s thoughts, perfectionism, inflated responsibility, overestimation of threat, and intolerance of uncertainty (Obsessive Compulsive Cognitions Working Group (OCCWG), 1997). Development of the Obsessive Beliefs Questionnaire (OBQ) which indexes the relative importance of each of these domains, enabled more systematic investigation of dysfunctional beliefs (OCCWG, 2001, 2003, 2005). When controlling for depression, threat estimation was found to be related to checking, neutralizing and washing symptoms. Control of thoughts was associated with obsessions, importance of thoughts was related to neutralizing, and perfectionism was related to ordering (Tolin, Woods & Abramowitz, 2003). Given the prominence of responsibility in cognitive-behavioural theories of OCD (Salkovskis, 1985, 1989), it was remarkable that this domain did not emerge as an independent predictor of OC symptoms. However, the study was conducted within a student sample and although the cognitive-behavioural theory of obsessions proposes that OCD symptoms occur on a continuum of severity and have their origin in largely normal human processes, OCD patients may differ from analogue participants in terms of the type and severity of symptoms (Tolin, et al., 2003). Investigation of a patient sample revealed significant associations between Responsibility and Threat Estimation and rumination scores, between Perfectionism and Certainty and checking and precision scores, and between

5 64 CHAPTER 4 Importance and Control of Thoughts and impulse scores, when controlling for depression and anxiety (Julien, O Connor, Aardema & Todorov, 2006). In the current study we attempted to replicate these findings in a patient sample. Furthermore, we added a clinician rated structured symptom checklist to the commonly used self-report instruments that were also used in previous studies in order to asses a wider variety of OCD symptoms. Before studying the specific associations, however, we first examined the structure of the Dutch version of the OBQ. Previous studies using the English version have shown some inconsistencies: An exploratory factor analysis on the OBQ resulted in three factors; Responsibility and Threat estimation, Perfectionism and Intolerance of Uncertainty, and Importance and Control of Thoughts (OCCWG, 2005). These three factors emerged in several other studies, but in different ways; as lower-order factors (Taylor, McKay & Abramowitz, 2005), or besides a large general factor (Woods, Tolin & Abramowitz, 2004). Therefore, it seems important to examine the factor structure of the Dutch version of the OBQ, before investigating associations between beliefs and subtypes. Method Participants One hundred and twenty-two participants (46M, 76F) who met DSM-IV-TR (American Psychiatric Association, 2000) criteria for OCD participated in the study. Mean duration of OCD was 18.9 years (SD, 12.1, range 1-63 years). Twenty patients never received treatment for their OC complaints, 96 patients received treatment for OCD at the time of the study or in the past, and for 5 patients no information was available. Comorbidity data was available for all patients; 15% of the patients evidenced a depression, 9% had a panic disorder, 8% had a simple phobia, 4% suffered PTSD, 11% evidenced general anxiety disorder, 3% hypochondriasis, and 3% had body dysmorphic disorder. Table 1 presents descriptive statistics on the sample s demographic variables, as well as means and standard deviations on symptomatology measures. Measures The MINI International Neuropsychiatric Interview (MINI-Plus) (Sheehan, Lecrubier, Harnett-Sheehan, Janavs, Weiller, Bonara, et al., 1997) is a structured DSM-IV/ ICD-10 interview, and was used for diagnosis. Psychometric properties are good (Sheehan, et al. 1997; Lecrubier, Sheehan, Weiller, Amorim, Bonara, Sheehan et al., 1997). To establish symptom severity, we used the Yale Brown Obsessive Compulsive Scale (Y-BOCS) (Goodman, Price, Rasmussen, Mazure, Fleischmann, Hill et al, 1989a; Goodman, Price, Rasmussen, Mazuro, Delagado, Heninger et al., 1989b), a clini-

6 OBSESSIVE BELIEFS AND OCD SYMPTOM DIMENSIONS 65 cian rated semi-structured interview consisting of 10 items measuring severity of obsessions (5 items) and compulsions (5 items) regardless of OCD subtype. Psychometric evaluation of the Dutch version in 65 psychiatric inpatients, showed excellent inter-rater agreement and internal consistency (Arrindell, Vlaming, Eisenhardt, Van Berkum & Kwee, 2002). The obsessions and compulsions dimensions inter-correlated low and showed different patterns of correlations with external measures, confirming divergent validity (Arrindell et al., 2002). The Y-BOCS is accompanied by the Y-BOCS Symptom Checklist which provides a list of 70 obsessions and compulsions, classified in 15 categories. Symptoms were rated present or not present. Furthermore, the Padua Inventory-Revised (PI-R) (Sanavio, 1988; Dutch version Van Oppen, 1992; Van Oppen, Hoekstra & Emmelkamp, 1995b) was administered to measure OCD symptomatology. The PI-R is a self-report questionnaire consisting of five subscales; impulses, washing, checking, rumination and precision. The validity, reliability and sensitivity to change are satisfactory (Van Oppen et al., 1995b). To measure OCD relevant beliefs the 44-item version of the Obsessive Beliefs Questionnaire (OBQ-44) (OCCWG, 1997, 2005; Dutch version Emmelkamp, Van Oppen & Wieringa, 1998) was administered. Psychometric validation of the OBQ-44 showed good internal consistency and criterion-related validity in clinical and non-clinical samples (OCCWG, 2005) The Spielbergers State-Trait Anxiety Inventory DY-2 (STAI-DY-2) (Spielberger, 1983) and the Beck Depression Inventory (BDI) (Beck, Rush, Shaw & Emery, 1979) were used to establish anxiety and depressive symptomatology. Procedure Patients of various mental health organizations in the northern part of the Netherlands were approached in the context of a genetic study into OCD, based on the diagnosis in their medical records. This was approved by the medical ethics committee of the University Medical Centre Groningen. Patients received extensive information about the study and were asked to return an informed consent form by mail if they wanted to participate. Subsequently, they received an invitation to attend the clinic for an interview in which DSM-IV axis-i disorders were screened. Furthermore, the Y-BOCS was administered and participants were asked to provide DNA by using a mouth-swab. Afterwards, participants received a questionnaire booklet which they could fill out at home and send back to the researcher. Statistical analysis First, we inspected the factor structure of the Dutch version of the OBQ-44 using the Multiple Group Method (MGM; e.g., Bernstein, 1988; Nunally, 1978). With this technique, subscales are defined as un-weighted sums of the item scores assigned

7 66 CHAPTER 4 Table 1. Demographic variables and measures of OCD, OC-beliefs, depression and anxiety Current study OCCWG, 2003, 2005 N M SD N M SD t Age ** Female 76 (62.3%) 56% Single 44 (36.1%) 52% Education Low 43 (35.2%) Medium 41 (33.6%) High 38 (31.2%) Y-BOCS Obsessions Compulsions Total * PI-R Impulses Washing Checking Rumination Precision Total *** OBQ-44 Importance and Control of Thoughts Responsibility and Threat estimation Perfectionism and Certainty ** *** * Total *** BDI STAI-trait OCCWG= Obsessive Compulsive Cognitions Working Group, Y-BOCS= Yale-Brown Obsessive Compulsive Scale, PI-R= Padua Inventory Revised, OBQ= Obsessive Beliefs Questionnaire, BDI= Beck Depression Inventory, STAI= State-Trait Anxiety Inventory, *p<.05, **p<.01, ***p<.001, 2-tailed

8 OBSESSIVE BELIEFS AND OCD SYMPTOM DIMENSIONS 67 to that subscale. Subsequently, correlations between each item and its subscale are calculated correcting for self-correlation, that is, the correlation between an item and the subscale that involves this item by using the item-rest correlation. If each item correlates highest with the subscale to which it is assigned, this indicates that the assignment is supported by the data, hence confirming the factor structure. Apart from being a simple, direct and understandable procedure, another advantage of MGM is that if an item seems to be assigned to the wrong factor, the procedure indicates to which factor the item should be assigned, according to the data. In a comparison of MGM and the more common Confirmatory Factor Analysis, it was shown that both methods were equally effective in recognizing a true assignment, however MGM was superior in recognizing false assignments (Stuive, Kiers, Timmerman & Ten Berge, 2008). In order to test whether beliefs were related to OCD symptom subtypes, we used both the Padua Inventory-Revised (PI-R) and the Y-BOCS Symptom Checklist (Y-CL) as dependent variables in multiple regression analyses. Before doing so, we conducted a Principal Components Analysis (PCA) on the Y-CL to obtain symptom dimensions which were used as measures for OC symptom subtypes. Since the scoring of the Y-CL resulted in binary data, tetrachoric correlations were computed. The correlations are obtained by hypothesizing the existence of a continuous latent variable underlying the dichotomy. These correlations were entered into the PCA. In order to determine the best factor solution, the eigenvalues of the components (indicating explained variance) were inspected using scree plots, taking into account the interpretability of the solutions. Varimax rotation was applied to the initial factor solutions. The analysis was conducted with LISREL 8.51 (Jöreskog & Sörböm, 2001). Subsequently, a multivariate multiple regression analysis was conducted to assess relationships between OC behaviours and OC beliefs. The PI-R subscales served as dependent variables, representing several different manifestations of OC symptoms, namely impulses, washing, checking, ruminating, and precision. The different dependent variables were used in a multivariate analysis to take into account their mutual relationships, thereby increasing statistical power (correlations between the dependent variables were moderately which is sufficient for multivariate analyses (Tabachnick & Fidell, 2007)). Gender, BDI, and STAI-trait were used as control variables and the OBQ-44 subscales as predictors. As post hoc analyses, hierarchical, univariate multiple regression analyses were conducted for each dependent variable separately. To assess relationships between beliefs and OC subtypes as measured by the Y-CL, hierarchical, univariate multiple regression analyses were performed using the uncorrelated Y-CL components, previously found in the PCA, as dependent variables. With the exception of the Principal Component Analysis on the Y-CL, all analyses were conducted using SPSS 11.5 (SPSS Inc., 2001).

9 68 CHAPTER 4 Results Factor structure of the Obsessive Belief Questionnaire Taking into account previously found high inter-correlations on the OBQ-44 subscales, we first calculated Pearson s correlation coefficients to determine the strength of association between the OBQ-44 subscales (see Table 2), which turned out to be high. The results of the Multiple Group Method analyses confirmed the three-factor structure suggested by the OCCWG (2005). Four of the 44 items did not show the highest correlations with their suggested subscales. However, differences between correlations were mostly small,.02 in three of four items. Inspection of the items contents did not suggest assignment to other subscales. Therefore, we adopted the original factor structure as the basis for computation of un-weighted subscales. Principal Component Analysis on the Y-BOCS Symptom Checklist The scree plot of the Principal Component Analysis (PCA) indicated a three- or a six-component solution. Based on exploration of both solutions, the three-component solution is used for interpretative reasons. Moreover, considering our sample size, it would be conceivable that the smaller factors in the six factor solution would not be replicated in another sample, whereas the three large factors can probably be considered as more stable symptom dimensions. The first factor represented obsessions about making mistakes, ordering, and hoarding, and compulsions related to checking, ordering and hoarding. The second factor represented items related to contamination and cleaning obsessions and compulsions. The third factor represented obsessions related to harming and sexuality. These three factors correspond to a large extent with the factors found by Baer (1994). Taking into account the sample size, we did not use the factor loadings for data analysis, since they would largely depend on characteristics of this sample. Instead of factor loadings, observed sum-scores were used. Associations between beliefs and OC symptom-subtypes: PI-R To assess relationships between OC behaviours and OC beliefs, a multivariate multiple regression analysis was conducted in which the PI-R subscales served as the dependent variables and the three OBQ-44 subscales found by the OCCWG (2005) as predictors. Gender, BDI, and STAI-trait were entered as control variables. The multivariate results showed no significant effect for gender, F (5,109)=1.3. Significant effects were found for all three OBQ-44 subscales; Importance and Control of Thoughts F (5,109)=6.5, p<.001, Responsibility and Threat Estimation F(5,109)=3.7, p<.01, and Perfectionism and Certainty F(5,109)=5.1, p<.001. Significant

10 OBSESSIVE BELIEFS AND OCD SYMPTOM DIMENSIONS 69 Table 2. Correlations among the OBQ-44 subscales Importance and Control of thoughts Responsibility and Threat estimation Importance and Control of thoughts Responsibility and Threat estimation Perfectionism and Certainty effects were also found for the BDI F(5,109)=2.8, p<.05, and the STAI F(5,109)=2.8, p<.05. Effect sizes were medium for BDI (η 2 p=.11) and STAI (η 2 p=.11), and large for the OBQ-44 subscales: Importance and Control of Thoughts η 2 p=.23, Responsibility and Threat Estimation η 2 p=.15, and Perfectionism and Certainty η 2 p=.19 (Cohen, 1977). The unique contribution of the OBQ factors was investigated using hierarchical multiple regression analyses for each PI-R subscale separately. First, gender, BDI, and STAI-trait together were entered as control variables. Next, the three OBQ-44 subscales were entered using a stepwise procedure. To assess the influence of the correlations between the independent variables (Table 2), VIF scores were computed (Variance Inflation Factor, see e.g., Stevens 2003). These were well within acceptable limits, indicating that multicollinearity was not a problem. Regression relationships are reported in Table 3. Results show that when controlling for gender and general distress, the Perfectionism and Certainty subscale was significantly associated with checking (t=3.36, p<.001), precision (t=3.78 p<.001), and ruminating (t=2.95, p<.005). Ruminating was furthermore significantly related to Responsibility and Threat Estimation (t=2.91, p<.005). Importance and Control of Thoughts was significantly associated with impulses (t=5.78, p<.001). No significant relationship was found between washing and any of the OBQ-44 subscales. The BDI however was significantly related to this subtype (t=3.48, p<.001). Since the residuals were not (approximately) normally distributed for the PI-R subscales Impulses, Washing, and Precision, transformations were conducted on these subscales. Since the distributions were negatively skewed, square root and cubic root transformations were used. Results of the multivariate multiple regressions after transformation were comparable to results before transformation: No significant effect for gender, and significant effects for all three OBQ-factors and for the STAI. The BDI showed a marginally significant multivariate effect with a p-value between 0.05 and 0.1. On a univariate level, OBQ-44 subscales were significantly related to the same PI-R subscales as before transformation. The STAI was significantly related to PI-R rumination, similar to before transformation. Since the BDI effect was nearly significant, univariate results were inspected, which showed a significant association between the BDI and washing. For all univariate tests a more stringent significance level of 0.01 was used, in order to control for multiple testing.

11 70 CHAPTER 4 Table 3. Results of multiple regression analyses with 3 OBQ-factors and control variables PI-R subscales Impulses Washing Checking Ruminating Precision Predictors b (SE) Beta R² R² change t Gender BDI STAI OBQ-ICT Gender BDI STAI Gender BDI STAI OBQ-PC Gender BDI STAI OBQ-PC OBQ-RT Gender BDI STAI OBQ-PC (.85).13 (.06) -.06 (.06).18 (.03) 1.47 (1.77).42 (.12) -.17 (.12).07 (1.31).06 (.09) -.07 (.09).11 (.03).19 (1.16).12 (.08).20 (.08).10 (.03).09 (.03) 2.35 (.98).07 (.07) -.03 (.07).10 (.03) ** *** *** *** ** 2.91** *** Note: b= unstandardized regression coefficient, SE= standard error, Beta=standardized regression coefficient, *p<.01, **p<.005, ***p<.001, ICT= Importance and Control of Thoughts, PC= Perfectionism and Certainty, RT= Responsibility and Threat estimation. Associations between beliefs and OC symptom-subtypes: Y-BOCS In order to test associations between beliefs and OC subtypes based on the Y-CL, the three factors extracted with the PCA were used separately as the dependent variables in hierarchical, univariate multiple regression analyses. Again, gender, BDI, and STAI-trait were used as control variables, and the three OBQ-subscales as predictors. Results showed no significant effect for any of the variables, neither predictor- nor control variables. This is remarkable considering the significant relationships found between beliefs and PI-R subscales.

12 OBSESSIVE BELIEFS AND OCD SYMPTOM DIMENSIONS 71 Discussion The purpose of this study was twofold. First, the structure of the Dutch version of the OBQ-44 was investigated in a patient sample. Second, relationships between dysfunctional beliefs and OC subtypes were examined. Concerning the factor structure of the Dutch version of the OBQ-44, our results confirmed the three factor structure as suggested by the OCCWG (2005). Given the high inter-correlations between these three factors, the existence of a more general underlying factor is very likely. However, considering the unique contributions of the OBQ-factors as predictors of OC symptoms, as found by the hierarchical regression analysis on the PI-R, one can conclude that the factors are distinct as well. Results of the hierarchical regression analysis, using the PI-R as a measure of OC symptoms, indicated specific relationships between dysfunctional beliefs and OC subtypes: Importance and Control of Thoughts was significantly related to impulses, Responsibility and Threat Estimation was significantly associated with rumination, and Perfectionism and Certainty was related to checking, rumination and precision. Interestingly, no cognitive predictor was found for washing. These findings are generally consistent with Julien et al. s study (2006), except that we found Perfectionism and Certainty to be related to rumination, whereas they did not. From a theoretical perspective, the relationship between checking and beliefs related to perfectionism and certainty is in line with the characteristic slowness, indecisiveness, and lack of confidence in memory. However, Rachman s (2002) cognitive theory of compulsive checking postulates responsibility to be very important in checking as well, which was not confirmed by our results. Furthermore, the association between Importance and Control of Thoughts and impulses is in line with findings on autogenous obsessions. Impulsive thoughts can be categorized as autogenous obsessions, which tend not to be associated with identifiable triggers, and are experienced as ego-dystonic (as opposed to reactive obsessions, which are triggered by identifiable external stimuli, and are perceived as more rational, such as thoughts of doubt about a mistake) (Lee & Kwon, 2003). In line with our findings, autogenous obsessions have been reported to be related to control of thoughts and importance of thoughts (Lee & Kwon, 2003). Interestingly, no association between beliefs and the subtype washing was found. Previous studies indicated evidence for two distinct washing subgroups: One group being characterized by patients who report feeling discomfort or feeling contaminated in OCD situations without fears of harm, whereas the other group consists of patients reporting specific fears of harm to self or others as a result of contamination (Calamari, Wiegartz, Rieman, Cohen, Greer, Jacobi, et al., 2004; Feinstein, Fallon, Petkova & Liebowitz, 2003). Dysfunctional beliefs might not be very relevant to the contamination subtype where there is just the experience of being contaminated without fear of harm to self or others. Since the PI-R does not distinguish between these types of washing, our group might contain both

13 72 CHAPTER 4 types, which might explain why we did not find significant associations between beliefs and this subtype. Besides studying the relationship between beliefs and self-reported OC symptoms, we also investigated associations between OBQ-44 subscales and symptom profile as assessed by a clinician-rated symptom checklist. In order to use the Y-CL as a measure of OC symptoms, we first analysed the structure of the Y-CL and found three factors: 1. obsessions about making mistakes, ordering, and hoarding, together with compulsions related to checking, ordering and hoarding, 2. contamination and cleaning obsessions and compulsions, 3. obsessions related to harming, and sexuality. By and large these three factors corresponded to the factors identified in previous research (e.g., Baer, 1994). Results of the regression analysis showed no significant relationships between specific beliefs and the above mentioned OC subtypes. In other words, these results do not provide evidence in support of the relationship between particular OC beliefs and OC symptom subtypes. Preliminary (unpublished) results of Rector and Szacun-Shimizu (2005), did not reveal significant relationships between beliefs and contamination or obsessionals either. The latter is remarkable, since one would expect harming-, and sexual obsessions to be related to importance and control of thoughts. In apparent contrast to the present study Rector and Szacun-Shimizu (2005) did find significant relationships between dysfunctional beliefs and hoarding and symmetry subtypes (respectively with Perfectionism and Certainty, and Importance and Control of Thoughts). These two symptom dimensions were represented in our first factor together with checking compulsions. The symptom diversity of our first factor might be an explanation for these divergent results. However, we used this factor solution, since we had a relatively small sample for factor analysis, and it was hypothesized that this small factor solution represented real symptom dimensions that could be replicated in other samples. Moreover, the three factors replicated Baer s (1994) factor solution. Overall, our results supported the existence of different OC relevant belief domains, and indicated specific relationships between certain dysfunctional beliefs and OC symptoms. This might be helpful to further characterize OC subtypes. However, an important limitation of the investigation of dysfunctional beliefs and their relation to OCD concerns the operationalization of beliefs. It might be problematic to assess the relevant beliefs by means of a questionnaire. First, since OCD is such a heterogeneous disorder, items of the OBQ-44 might not be sufficiently idiosyncratic. In addition, particular target beliefs might only be experienced as highly believable in an OCD-relevant context, whereas these beliefs may be considered as unbelievable and/or irrelevant in a non OCD context (e.g., when filling out the questionnaire in a lab). Finally, it cannot be ruled out that there are other relevant belief domains that are not assessed by the OBQ-44. Subtyping research is dominated by two methodologies; cluster-analysis and factor-analysis. Factor-analysis yields dimensions, whereas clustering provides exclusive categories, and at the present time it is unclear whether OCD is better regarded as dimensional or categorical (Radomsky & Taylor, 2005). In this study

14 OBSESSIVE BELIEFS AND OCD SYMPTOM DIMENSIONS 73 we relied on factor-analysis which takes into account the continuum of disorder severity. However, considering recent findings which revealed that a substantial proportion of OCD patients scored similar to normal controls on the OBQ-44 (Calamari, Cohen, Rector, Szacun-Shimizu, Riemann & Norberg, 2006; Taylor, Abramowitz, McKay, Calamari, Sookman, Kyrios, et al., 2006), and previously reported indications of two different washing subtypes, future studies might benefit from describing OCD clusters based on symptom presentation and relevance of beliefs. Furthermore, additional factors could be included like inverse inference (the tendency to negate reality on the basis of subjective possibilities), which is postulated to be characteristic of cognitive reasoning in OCD (Aardema, O Connor, Emmelkamp, Marchand & Todorov, 2005), just right experiences (Coles, Frost, Heimberg & Rhéaume, 2003), and features like age at onset and history of tics. To conclude, the present study clearly showed specific associations between beliefs and OC symptoms as measured by a self-report questionnaire, whereas no relationships were found between beliefs and OC symptoms assessed by a clinician rated checklist. Future studies are necessary to further characterize OC subtypes. The relevance of such enterprise not only resides in improving aetiological theory but may eventually also improve treatment possibilities for this highly invalidating disorder.

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