Background: Problems in Instrumental Activities of Daily Living (IADL) can arise before cognitive impairment, but not all activities are affected to the same degree. Earliest IADL problems are likely episodic and context-dependent, requiring a measurement method that can detect these features.

Ecological Momentary Assessment (EMA) can capture temporal variability in IADL functioning and the potential impact of contextual factors, e.g., fatigue. EMA content should be carefully selected and tailored to the outcome of interest and population.

Study aims: This study aimed 1) to provide a set of items suitable for EMA of IADL in individuals with SCD, based on clinical relevance and best psychometric features, and 2) perform a preliminary exploration of day-to-day variability in self- and study partner reported IADL functioning and experienced cognition.

Conclusions: Relevant items for frequent (EMA) measurement of IADL in SCD reflect complex activities across a variety of IADL domains. Preliminary results suggest substantial self- and proxy-reported day-to-day variability for the degree of cognitive complaints, suggesting retrospective questionnaires may miss relevant signal, but less for IADL functioning (traffic, smartphone use). Potential differences in day-to-day fluctuations between reporters in SCD and associations with contextual factors need to be further investigated.