The incidence of mild cognitive impairment: A systematic review and data synthesis

INTRODUCTION: Incidence estimates of mild cognitive impairment (MCI) range widely. We obtained contemporary age-specific MCI incidence rates and examined sources of heterogeneity. METHODS: We conducted a systematic review of population-based studies from the Americas, Europe, and Australia using restrictive inclusion criteria to limit heterogeneity. Incidence was examined using 5-year age categories for MCI and amnestic/nonamnestic subtypes. Data were synthesized using quantitative and qualitative descriptive analyses and quantitative meta-analyses. RESULTS: Meta-analysis estimates (95% CI) of MCI incidence per 1000 person-years were 22.5 (5.1–51.4) for ages 75–79y, 40.9 (7.7–97.5) for ages 80–84y, and 60.1 (6.7–159.0) for ages 85+y. Despite restrictive inclusion criteria, considerable heterogeneity (measured by I(2)) remained. Meta-analysis findings and simple descriptive statistics were consistent and supported by qualitative review. DISCUSSION: Heterogeneity in MCI incidence estimates persisted across age-specific estimates from population samples, likely reflecting differences in populations and methods. Incidence rate ranges are important to consider with summary point estimates.