Abstract
The practice of medicine relies on the patient-physician relationship, knowledge, and clinical judgment. Randomized controlled trials (RCTs) remain the least biased method for studying the effects of interventions in selected populations and are the only method to control adequately for unknown confounders. However, physicians face the limitations of RCTs on a daily basis as they treat relatively unselected populations and individual patients. We explore the benefits and limitations of RCTs for some neurologic disorders, and discuss the difficulties of predicting individualized outcomes and anticipating treatment responses in those heterogeneous conditions. Observational studies and advances in understanding neurologic diseases complement RCTs in decision-making. Considerable challenges remain for personalized medicine; for now, clinicians must rely on their ability to integrate evidence and clinical judgment.