Study on Age-Period-Cohort Effects of Cognitive Abilities among Chinese Older Adults based on the Cognitive Reserve Hypothesis

Abstract Background Cognitive abilities are key indicators of healthy aging. Nowadays, China has gradually entered a stage of deep aging, and the elderly population with age-relate cognitive decline has significantly increased. However, previous research on cognitive abilities based on long-term time trends has been relatively few among Chinese older adults. This study aims to explore the cognitive abilities changes and group differences among Chinese older adults aged 65 to 105 based on three-time dimensions of age, period, and birth cohort. Methods The 8 waves of Chinese Longitudinal Healthy Longevity Survey (CLHLS) are used from 1998 to 2018. To avoid perfect collinearity in the time dimension, the study employ Hierarchical APC-Cross-Classified Random Effects Model (HAPC-CCREM) to examines age-period-cohort effects on the cognitive abilities among Chinese older adults. the age is set as fixed-effect, while the period and birth cohorts are set as random-effect, and explore the significant factors that impact the cognitive abilities of Chinese older adults based on the Cognitive Reserve Hypothesis. Results At the fixed-effect level, demographics factors, health behaviors, self-rated health, subjective well-being and childhood adversity significantly impact cognitive ability among Chinese older adults. Age effects are significant, and cognitive abilities show an inverted “U”-shaped curve with age. At the random-effect level, period effects are significant, with the overall cognitive levels show a gradual annual increase among Chinese older adults Since 2008. Cohort effects are also significant, where the overall cognitive levels of the earlier-born cohorts in the first six groups show an increasing trend. Conversely, the overall cognitive levels of later-born cohorts in the latter five groups show a declining trend. Notably, the period effects significantly promote the cohort effects. Conclusions The Cognitive Reserve Hypothesis support the significance of the majority of impacting factors. the cognitive abilities show an accelerating decline with increasing age, following an evolutionary trajectory in accordance with physiological principles among Chinese older adults. The cognitive abilities show a monotonic increasing trend year by year since 2008, further validating the Flynn effect among Chinese older adults. The first six earlier-born cohorts show an increasing trend in cognitive abilities, supporting the hypothesis of pathological state compression. Therefore, the cognitive abilities of the five later-born cohorts show a declining trend, supporting with the hypothesis of pathological state expansion.