SwissDEM used a one-phase, population-based, cross-sectional design, based on the 10/66 Dementia Research Group protocol. Data were collected through structured face-to-face and telephone interviews with participants (aged 65+) and, for each participant, a designated informant (a family member or close acquaintance).
Participants were identified through age- and sex-stratified random sampling from official population registries (Swiss Federal Office of Statistics). Selected individuals received an informative letter followed two weeks later by an invitation letter; they could register to participate via online form (REDCap), paper-based form, phone, or email. In Zurich, recruitment leveraged an existing cohort infrastructure (Corona Immunitas).
All questionnaires and assessments were administered electronically via REDCap, a data collection platform hosted on USI servers (Lugano), accessible on tablets, smartphones, and laptops. Trained interviewers (non-clinicians) conducted the interviews, which lasted approximately 45 minutes with the participant and 15–30 minutes with the informant, either at the participant's home, a nursing home, or another location of the participant's choosing.
The interview had a modular structure covering informed consent, psychological dimensions, economic impact and risk/protective factors, cognitive assessment of the participant, and, for informants, proxy-rated cognition, neuropsychiatric symptoms, dementia severity, caregiver burden, social cognition, and care arrangements. Interviewers received standardized, manualized training and were periodically supervised for data quality. The electronic system included built-in validation checks and alerts for implausible or incomplete entries, with automated data transfer and encrypted storage. Written informed consent was obtained from all participants (or their legal representative in case of impairment) prior to any study procedure.
