Considerations for the use of the Informant Questionnaire on Cognitive Decline in the Elderly (IQCODE) in cross-country comparisons of cognitive aging and dementia

INTRODUCTION: Informant reports are a critical component of dementia diagnoses, but the comparability of informant reports across countries is not well understood. METHODS: We compared the performance of the Informant Questionnaire on Cognitive Decline in the Elderly (IQCODE) using population-representative surveys in the United States (N = 3183), England (N = 1050), and India (N = 4047). RESULTS: Analyses of regression splines and comparisons of model fit showed strong associations between IQCODE and objective cognition at low cognitive functioning in the United States and England; in India, the association was weaker but consistent over the range of cognition. Associations between IQCODE score and informant generation (analysis of variance [ANOVA] p = 0.001), caregiver status (p < 0.001), and years known by the informant (p = 0.015) were different across countries after adjusting for objective cognition. DISCUSSION: In India, the IQCODE was less sensitive to impairments at the lowest levels of cognitive functioning. Country-specific adjustments to IQCODE scoring based on informant characteristics may improve cross-national comparisons.