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) 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.