Age-related selection bias in Parkinson's disease research: are we recruiting the right participants?

Objective: To describe, and explore heterogeneity in, age at onset/diagnosis in Parkinson's disease (PD) and compare mean age at onset/diagnosis in incidence studies with that in general PD research studies.

Methods: We systematically reviewed studies of PD incidence. We meta-analysed mean age at onset/diagnosis and age-stratum-specific incidence rates.