The latent variable structure of the Compulsive Behaviour Checklist in people with Prader-Willi syndrome

The presence and severity of compulsive behaviours may be evaluated via the Compulsive Behaviour Checklist (CBC) and this instrument has been successf ully employed in people with intellectual disability. However, the applicab ility of the overall CBC scoring system, which entails tallying the number of behavioural categories represented (i.e. five) as well as the number of individual behaviours endorsed (i.e. 25), is not known in the population wi th Prader-Willi syndrome (PWS). The present investigation examined the late nt variable structure of the CBC in people with PWS in order to identify po ssible population-specific scoring and interpretation considerations. The 2 5 behaviour-specific. items of the CBC were analysed for 75 people with PWS (44 females and 31 males) aged between 4 and 41 years (mean +/- SD = 11.4 +/- 9.4) via factor analysis with principal component extraction and equama x rotation. The most suitable solution was determined on the basis of multi ple empirical criteria: (I) the scree test; (2) eigenvalues > 1.00; (3) sal ient loadings > 0.30; (4) the clarity of item assignment to a single latent dimension; (5) the internal consistency of the latent dimension(s) (coeffi cient alpha greater than or equal to 0.70); and (6) item-total correlations between 0.20 and 0.79. In addition, solutions were examined with respect t o psychological theory and previous research. A 'general factor' (i.e. sing le latent dimension) solution which adhered to all a priori criteria was in dicated. Twenty-four out of 25 items achieved salient loadings ranging from 0.46 to 0.80 on the general factor. The single item which failed to achiev e salience,'deviant grooming-skin picking', exhibited both substantial uniq ue variance (0.997) and moderate reliability (r = 0.59, P < 0.001). The int ernal consistency of the general factor was strong (alpha = 0.93) and all s alient items were suitably correlated with the unit-weighted total score (r (item-total) = 0.41-0.77). The traditional CBC scoring system, which includ es tallying the number of categories represented, would not be relevant in this PWS sample. In addition, the recommended tallying of the number of ind ividual behaviours endorsed does not reflect the empirically indicated noti on of compulsive behaviour in this special population. These findings indic ate that the 24 salient items should be scored as a unit-weighted composite and that the score on the substantially unique item (skin picking) should be considered a separate measure when evaluating compulsive behaviours via the CBC in people with PWS.