[A study of the psychometric properties of the Icelandic translation of Obsessive Thoughts Checklist (OTC) with confirmatory factor analysis]

J Smári, D Thor Olason
L'Encéphale 2005, 31 (2): 144-51
The Obsessive Thoughts Checklist (OTC) differs from several other measures of obsessive-compulsive symptoms in its focus on obsessive thoughts instead of compulsive behaviour. The OTC has been used in several studies in France and abroad and support for the discriminant and convergent validity of the instrument has been gathered. The authors of the OTC recently reported 3 underlying factors in this instrument: a perfectionism/verification factor, a contamination factor and a responsibility factor. In an earlier study of the OTC a 2 factor solution was however suggested. It therefore seems important to further elucidate the factorial structure of this instrument using confirmatory factor analysis. In this study data on the Icelandic translation of the OTC from three samples of Icelandic college students were submitted first to an exploratory and then to a confirmatory factor analysis. The total number of subjects was 614 college students, 254 men and 360 women with a mean age of 24.4 (sd = 5.0). The results of the exploratory factor analysis (PCA) submitted to a varimax rotation are presented in table I. The 3 expected factors were reproduced with few cross-loadings. In the confirmatory factor analysis the fit of three models to the data were evaluated: a 1 factor model, the 2 factor model of Bouvard et al. and the 3 factor model of Bouvard et al.. An initial examination of the data led to logarithmic transformation of 18 items to reduce skewness in their distributions. The data was subsequently subjected to a confirmatory factor analysis to compare the three-factor model with the two-factor and one-factor models for the OTC. The factors for the three- and two-factor models were allowed to correlate freely. The data were analysed using the EQS procedure, and the models tested were covariance structure models. Table II presents the goodness of fit indices for all three models. The results show that none of the three models provide an overall appropriate fit for the data. However, the fit indices for the three-factor model were considerably higher than found for the two or one factor models and the RMSEA index for the three-factor model suggested an acceptable fit for that model. Although the three-factor model suggests the best fit of all three models, the fit indices were still unacceptably low. Further examination of the data revealed a pattern of standardized residuals suggesting that this might in part be attributable to three items from the responsibility factor (items 26, 19 and 15) not being well specified within the model. When the residuals for these items were allowed to correlate, the fit of the model was substantially improved (CFI = 0.85; GFI = 0.87; AGFI = 0.85; RMSEA = 0.062). This indicates that a revision of the responsibility scale might be appropriate. Table III provides the means, standard deviations and the alpha coefficients for the 3 subscales of the OTC as well as for the total scale. In one subsample of the study (sample 1, n = 169) the OTC was administered together with the Padua Inventory-Washington State Revision (PI-WSUR) measuring obsessive-compulsive symptoms, the Penn State Worry Questionnaire (PSWQ) and the Community Epidemiological Scale-Depression (CES-D) measuring depression. In order to investigate the convergent validity and divergent of the OTC its correlation with the PI-WSUR was compared with its correlations with PSWQ and CES-D. These correlations shown in table IV support the convergent and divergent validity of the OTC. In another subsample of the study (sample 2, n = 296) the OTC was administered together with the Maudsley Obsessive Compulsive Inventory (MOCI). For samples 1 and 2, zero order and partial correlations were calculated between the subscales of the OTC and the subscales of the other instruments. As shown in table V the strongest correlations between the checking/perfectionism and the contamination subscales of the OTC were with corresponding subscales of the PI-WSUR and the MOCI. It is concluded that the factorial, the convergent and the divergent validities of the Icelandic translation of the OTC are supported in a student population even though the somewhat suboptimal fit of the three-factor model may indicate that a revision of the responsibility factor might be in order. This should however be further studied in a clinical population.

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