Multigroup Confirmatory Factor Analysis of the Cognitive Dysfunction Questionnaire: instrument refinement and measurement invariance across age and sex. 
The study adopted Confirmatory Factor Analysis (CFA) to investigate the factorial structure and reduce the number of items of the Cognitive Dysfunction Questionnaire (CDQ).  The analyses were based on data for a total of 1,115 participants from population based samples (mean age: 63.0 ± 14.5 years, range: 25-95) randomly split into a refinement (N = 569) and a cross-validation (N = 546) sample.  Equivalence of the measurement and structural portions of the refined model was demonstrated across the refinement and cross-validation samples.  Among competing models the best fitting and parsimonious model had a hierarchical factor structure with five first-order and one second-order general factor.  For the final version of the CDQ, 20 items within five domains were selected (Procedural actions, Semantic word knowledge, Face recognition, Temporal orientation, and Spatial navigation).  Internal consistency reliabilities were adequate for the total scale and for the subscales.  Multigroup CFAs indicated measurement invariance across age and sex up to the scalar level.  Finally, higher levels of cognitive dysfunction as reflected by CDQ scores were predicted by advancing age, fewer years of education, and with deficits in general cognitive functioning as reflected by scores on the Mini-Mental State Examination.  In conclusion, the CDQ appears to be psychometrically sound and shows the expected relationships with variables known to be associated with cognitive dysfunction and dementia.  Future studies should apply it among clinical groups to further test its usefulness.