Estimation of events in cohort studies based on probability of cognitive impairment.

BackgroundDementia and Alzheimer's disease-causing pathologies progress slowly over decades, and participants are recruited cognitively intact, so designing studies to observe enough cases within a feasible timeframe is important.ObjectiveIn this study, we used readily available basic predictors, age, family history, sex, and apolipoprotein E () 4 allele carriership, to generate cumulative incidence functions for serious cognitive impairments over years of follow-up.MethodsThe data were taken from the University of Kentucky Alzheimer's Disease Research Center longitudinal cohort established in 1989. The participants were recruited cognitively unimpaired and aged 60+. The probability of serious cognitive impairment was assessed using a multinomial logistic model, with age, the number of risk factors (family history and 4 allele) and sex as predictors.ResultsWe estimated that when two or more risk factors are present, the long-term incidence of clinical mild cognitive impairment and dementia is 2.3 to 2.7 times higher than that of the 0-risk group for both sexes, whereas the 0-risk group experienced approximately 7.9% to 11.6% longer observation times for female and 0.9% to 4.8% for male compared to the two or more risks group.ConclusionsThis study presents the expected cumulative incidence functions over varying follow-up times, and the expected observation time of serious cognitive impairment for given family history, carriership of 4, age and sex.