Harmonized Cognitive Assessment Protocol: What makes an HCAP an HCAP? An adaptive architecture for measuring cognitive aging around the world

Objectives: Harmonized cognitive batteries are crucial for studying cognitive impairment and dementia in aging populations globally. Challenges persist in administering them in a way that maintains both cross-national comparability and local validity to measure cognitive functioning across settings. In this perspective, we review the approach undertaken in the Harmonized Cognitive Assessment Protocol (HCAP) network of studies and propose that the core identity of the HCAP lies not in a fixed set of tests but in a fixed-flexible, cross-culturally adaptive measurement architecture. Methods: Via expert engagement, we examined the evolving goals of HCAP studies, delineated necessary study settings, and outlined domain-specific recommendations for cognitive assessments. Results: To balance high-quality measurement of cognitive domains and maintain the ability to perform meaningful cross-national comparisons, each HCAP should include a common set of at least three to four continuously distributed test items per domain that can link domains across studies. We present candidate tests and offer recommendations for domains of memory, executive functioning, language, visuospatial ability, and orientation. We discuss considerations for HCAP studies regarding appropriate sampling, test battery length of at least one hour, interviewer training, and missing data handling. Discussion: We advocate for the HCAP as a structured yet adaptable framework that prioritizes measurement precision and cultural relevance, while retaining sufficient uniformity to conduct statistical harmonization across settings. What makes an HCAP an HCAP is not a strict checklist of tests, but a commitment to rigorous, culturally respectful measurement of cognitive health in older adults around the world.