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Table 1 Grading system for quality of evidence

From: Vascular risk factors and Alzheimer's disease: are these risk factors for plaques and tangles or for concomitant vascular pathology that increases the likelihood of dementia? An evidence-based review

Grade of evidence Sampling Design Information
A1 Representative Longitudinal prospective Clinical and autopsy
A2 Non-representative Longitudinal prospective Clinical and autopsy
B1 Representative Longitudinal prospective Clinical only
B2 Non-representative Longitudinal prospective Clinical only
C1 Representative Cross-sectional Clinical and autopsy
C2 Non-representative Cross-sectional Clinical and autopsy
D1 Representative Cross-sectional Clinical only
D2 Non representative Cross-sectional Clinical only