Estimating prevalence of subjective cognitive decline in and across international cohort studies of aging: a COSMIC study
Susanne Röhr, Alexander Pabst, Steffi G. Riedel‐Heller, Frank Jessen, Yuda Turana, Yvonne Suzy Handajani, Carol Brayne, Fiona E. Matthews, Blossom C. M. Stephan, Richard B. Lipton, Mindy J. Katz, Cuiling Wang, Maëlenn Guerchet, Pierre‐Marie Preux, Pascal Mbélesso, Karen Ritchie, Marie‐Laure Ancelin, Isabelle Carrière, Antonio Guaita, Annalisa Davin, Roberta Vaccaro, Ki Woong Kim, Ji Won Han, Seung Wan Suh, Suzana Shahar, Normah Che Din, Divya Vanoh, Martin P.J. van Boxtel, Sebastian Köhler, Mary Ganguli, Erin Jacobsen, Beth E. Snitz, Kaarin J. Anstey, Nicolas Cherbuin, Shuzo Kumagai, Sanmei Chen, Kenji Narazaki, Tze Pin Ng, Qi Gao, Xinyi Gwee, Henry Brodaty, Nicole A. Kochan, Julian N. Trollor, António Lobo, Raúl López‐Antón, Javier Santabárbara, John D. Crawford, Darren M. Lipnicki, Perminder S. Sachdev
Abstract
BACKGROUND: Subjective cognitive decline (SCD) is recognized as a risk stage for Alzheimer's disease (AD) and other dementias, but its prevalence is not well known. We aimed to use uniform criteria to better estimate SCD prevalence across international cohorts. METHODS: We combined individual participant data for 16 cohorts from 15 countries (members of the COSMIC consortium) and used qualitative and quantitative (Item Response Theory/IRT) harmonization techniques to estimate SCD prevalence. RESULTS: The sample comprised 39,387 cognitively unimpaired individuals above age 60. The prevalence of SCD across studies was around one quarter with both qualitative harmonization/QH (23.8%, 95%CI = 23.3-24.4%) and IRT (25.6%, 95%CI = 25.1-26.1%); however, prevalence estimates varied largely between studies (QH 6.1%, 95%CI = 5.1-7.0%, to 52.7%, 95%CI = 47.4-58.0%; IRT: 7.8%, 95%CI = 6.8-8.9%, to 52.7%, 95%CI = 47.4-58.0%). Across studies, SCD prevalence was higher in men than women, in lower levels of education, in Asian and Black African people compared to White people, in lower- and middle-income countries compared to high-income countries, and in studies conducted in later decades. CONCLUSIONS: SCD is frequent in old age. Having a quarter of older individuals with SCD warrants further investigation of its significance, as a risk stage for AD and other dementias, and of ways to help individuals with SCD who seek medical advice. Moreover, a standardized instrument to measure SCD is needed to overcome the measurement variability currently dominant in the field.