Figure 1. Data sources and sampling.
All patients with TBI and a 2% random sample of all patients who met the specified inclusion criteria were identified from the nationwide VHA NPCD and the CTBIE database. A 1:1 age matching of patients with and without TBI was then performed for a final study cohort of 325,870 patients. CTBIE = Comprehensive Traumatic Brain Injury Evaluation; NPCD = National Patient Care Database; PD = Parkinson disease; TBI = traumatic brain injury; VHA = Veterans Health Administration.