The Cognitive Online Self‐Test Amsterdam (COST‐A): Establishing norm scores in a community‐dwelling population

Visser, Leonie N.C.; Dubbelman, Mark A.; Verrijp, Merike; Wanders, Lisa; Pelt, Sophie; Zwan, Marissa D.; Thijssen, Dick H.J.; Wouters, Hans; Sikkes, Sietske A.M.; van Hout, Hein P.J.; van der Flier, Wiesje M.

BACKGROUND: Heightened public awareness about Alzheimer's disease and dementia increases the need for at‐home cognitive self‐testing. We offered Cognitive Online Self‐Test Amsterdam (COST‐A) to independent groups of cognitively normal adults and investigated the robustness of a norm‐score formula and cutoff. METHODS: Three thousand eighty‐eight participants (mean age ± standard deviation = 61 ± 12 years, 70% female) completed COST‐A and evaluated it. Demographically adjusted norm scores were the difference between expected COST‐A scores, based on age, gender, and education, and actual scores. We applied the resulting norm‐score formula to two independent cohorts. RESULTS: Participants evaluated COST‐A to be of adequate difficulty and duration. Our norm‐score formula was shown to be robust: ≈8% of participants in two cognitively normal cohorts had abnormal scores. A cutoff of ‐1.5 standard deviations proved optimal for distinguishing normal from impaired cognition. CONCLUSION: With robust norm scores, COST‐A is a promising new tool for research and clinical practice, providing low cost and minimally invasive remote assessment of cognitive functioning.