Intracranial Hemorrhage, Traumatic

The goal is to derive and a clinical decision rule for safe exclusion of traumatic brain injury without neuroimaging in head-injured ED patients who take anticoagulant medications. The objectives are to: 1. Derive and externally validate a new highly sensitive and maximally specific clinical decision rule for the exclusion of traumatic brain injury in head-injured ED patients who take anticoagulant medications; and, 2. Estimate the sensitivity and specificity of existing head injury clinical decision rules in head-injured ED patients who take anticoagulant medications.