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Objectives Age-related differences in cognition are typically assessed by comparing groups of older to younger participants, but little is known about the continuous trajectory of cognitive changes across age, or when a shift to older adulthood occurs. We examined the pattern of mean age differences and variability on episodic memory and executive function measures over the adult lifespan, in a more fine-grained way than past group or lifespan comparisons. Methods We used a sample of over 40,000 people aged 18-90 who completed psychometrically validated online tests measuring episodic memory and executive functions (the Cogniciti Brain Health Assessment). Results Cognitive performance declined gradually over adulthood, and rapidly later in life on spatial working memory, processing speed, facilitation (but not interference), associative recognition, and set shifting. Both polynomial and segmented regression fit the data well, indicating a non-linear pattern. Segmented regression revealed a shift from gradual to rapid decline occurred in the early sixties. Variability between people (interindividual variability or diversity) and variability within a person across tasks (intraindividual variability or dispersion) also increased gradually until the sixties, and rapidly after. Confirmatory factor analysis revealed a single general factor (of variance shared between tasks) offered a good fit for performance across tasks. Discussion Lifespan cognitive performance shows a non-linear pattern, with gradual decline over early and mid-adulthood, followed by a transition in the sixties to notably accelerated, but more variable, decline. Some people show less decline than others, and some cognitive abilities show less within-person decline than others.

Introduction More women than men develop Alzheimer's disease, yet women perform better and show less decline on episodic memory measures, a contradiction that may be accounted for by modifiable risk factors for dementia. Methods Associations among age, sex, modifiable dementia risk factors, and cognition were measured in a cross‐sectional online sample ( n = 21,840, ages 18 to 89). Results Across four tests of associative memory and executive functions, only a Face‐Name Association task revealed sex differences in associative memory that varied by age. Men had worse memory than women (the equivalent of performing similar to someone 4 years older) across ages. Men had larger age differences than women (ie, worse memory in older ages) among people with no to one risk factor, but not those with multiple risk factors. Discussion Because the relationship between dementia risk factors and age‐related memory differences varies between men and women, sex‐specific dementia prevention approaches are warranted.

Background Reversible lifestyle behaviors (modifiable risk factors) can reduce dementia risk by 40%, but their prevalence and association with cognition throughout the adult lifespan is less well understood. Methods The associations between the number of modifiable risk factors for dementia (low education, hypertension, hearing loss, traumatic brain injury, alcohol or substance abuse, diabetes, smoking, and depression) and cognition were examined in an online sample (N = 22,117, ages 18–89). Findings Older adults (ages 66–89) had more risk factors than middle‐aged (ages 45–65) and younger adults (ages 18–44). Polynomial regression revealed that each additional risk factor was associated with lower cognitive performance (equivalent to 3 years of aging), with a larger association as age increased. People with no risk factors in their forties to seventies showed similar cognitive performance to people 10 or 20 years younger with many risk factors. Interpretation Modifiable dementia risk factors amplify lifespan age differences in cognitive performance.

Background: Modifiable lifestyle behaviours can reduce dementia risk by 40%, but their prevalence and association with cognition throughout the adult lifespan is less well understood. Methods: Associations between eight modifiable risk factors for dementia (low education, hypertension, hearing loss, traumatic brain injury, alcohol or substance abuse, diabetes, smoking, and depression) and cognition were examined in an online sample (N = 22,117, aged 18-89). Findings: Older adults (ages 66-89) had more risk factors than middle-aged (ages 45-65) and younger adults (ages 18-44). Polynomial regression revealed each additional risk factor was associated with a drop in cognitive performance (equivalent to three years of aging), with a larger association as age increased. People with no risk factors in their forties to seventies showed similar cognitive performance to people ten or twenty years younger with many risk factors. Interpretation: Modifiable dementia risk factors may be more important than age in predicting cognitive performance.

INTRODUCTION: More women than men develop Alzheimer’s disease, yet women show less age-related episodic memory decline, a contradiction that may be accounted for by modifiable risk factors for dementia. METHODS: Associations between sex, modifiable dementia risk factors, and cognition were measured in a cross-sectional online sample (n = 21,840, ages 18-89). RESULTS: Across four tests of associative memory and executive functions, only a Face-Name Association task revealed sex differences in age-related decline. Men had worse associative memory than women (the equivalent of four years of aging). Each additional risk factor had the equivalent of three and a half years of aging. Men had greater age-related decline in associative memory than women among those with no to one risk factors, but multiple risk factors eliminated the female advantage. DISCUSSION: Because the relationship between dementia risk factors and age-related memory decline differs for men and women, sex-specific dementia prevention approaches are warranted.

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Introduction: Mean cognitive performance is worse in amnestic mild cognitive impairment (aMCI) compared to control groups. However, studies on variability of cognitive performance in aMCI have yielded inconclusive results, with many differences in variability measures and samples from one study to another.Methods: We examined variability in aMCI using an existing older adult sample (n=91; 51 with aMCI, 40 with normal cognition for age), measured with an online self-administered computerized cognitive assessment (Cogniciti's Brain Health Assessment). Our methodology extended past findings by using pure measures of variability (controlling for confounding effects of group performance or practice), and a clinically representative aMCI sample (reflecting the continuum of cognitive performance between normal cognition and aMCI).Results: Between-group t-tests showed significantly greater between-person variability (interindividual variability or diversity) in overall cognitive performance in aMCI than controls, with a small to moderate effect size, d = 0.44. No significant group differences were found in within-person variability (intraindividual variability) across cognitive tasks (dispersion) or across trials of a response time task (inconsistency), which may be because we used a sample measuring the continuum of cognitive performance. Exploratory correlation analyses showed that a worse overall score was associated with greater inter-and intraindividual variability, and that variability measures were correlated with each other, indicating people with worse cognitive performance were more variable.Discussion: The current study demonstrates that self-administered online tests can be used to remotely assess different types of variability in people at risk of Alzheimer`s. Our findings show small but significantly more interindividual differences in people with aMCI. This diversity is considered as 'noise' in standard assessments of mean performance, but offers an interesting and cognitively informative 'signal' in itself.