Re-assessing the dimensional structure of the Informant Questionnaire on Cognitive Decline in the Elderly (IQCODE): empirical evidence for a shortened Brazilian version

BACKGROUND: The dimensional structure, effective number of item responses and item redundancies are controversial features of the Informant Questionnaire on Cognitive Decline in the Elderly (IQCODE) requiring more light. The aims of the present study are to revisit the dimensional structure and propose a shorter version of the instrument. METHODS: The sample comprised 652 elderly and their informants, either attending a geriatric service of a public university clinic or enrolled in a health care provider database in Rio de Janeiro, Brazil. A Confirmatory Factor Analysis (CFA) first tested the originally proposed one-dimensional structure comprised of 26 items. This was followed by sequential Exploratory Structural Equation Model (ESEM) to evaluate alternative models, in particular a bi-dimensional solution. The identification of residual correlations (RC) lead to a shortened 20-item model, which was tested further via CFA. RESULTS: The original model fitted poorly (RMSEA = 0.073; 90 % CI: 0.069-0.077). Regarding the two-dimensional model, the exploratory procedure (ESEM) indicated several RCs and a lack of factor-based discriminant validity. The ensuing CFA on the one-dimensional model with freely estimated RCs showed an adequate fit (RMSEA = 0.051; 90 % CI: 0.047-0.055). Addressing the identified RCs, the CFA on the abridged 20-item version also showed an adequate fit (RMSEA = 0.058; 90 % CI: 0.053-0.064) and no further RCs. CONCLUSION: A one-factor dimensional structure and a reduced version with 20 locally independent items were the most tenable solution. However, although promising, this simpler structure requires further examination before it may be fully supported and recommended.