RESUMEN
INTRODUCTION: Impaired cognition and instrumental activities of daily living (iADL) are key diagnostic features of dementia; however, few studies have compared trajectories of cognition and iADL. METHODS: Participants from the IDEAL study comprised 1537, 1183, and 851 people with dementia, and 1277, 977, and 749 caregivers at baseline, 12 and 24 months, respectively. Addenbrooke's Cognitive Examination-III and Functional Activities Questionnaire were used to measure cognition and iADL, respectively. Scores were converted to deciles. RESULTS: Self-rated iADL declined on average by -0.08 (-0.25, 0.08) decile points per timepoint more than cognition. Informant-rated iADL declined on average by -0.31 (-0.43, -0.18) decile points per timepoint more than cognition. DISCUSSION: Cognition and self-rated iADL declined at a similar rate. Informant-rated iADL declined at a significantly greater rate than cognition. Therefore, either cognition and perceived iADL decline at different rates or informants overestimate increasing iADL difficulties compared to both cognition and self-ratings. HIGHLIGHTS: Self-ratings of the degree of functional difficulties were consistent with cognition Decline in self-rated everyday activities was consistent with cognitive decline Informant-ratings of everyday activities declined more than cognition.