Only a small fraction of carefully selected patients are allowed to enroll in randomised controlled trials involving new compounds – the gold standard of drug assessment. But trying to acquire the most significant efficacy and safety results for a new drug is one goal, treating patients every day in hospitals or practices with it is something else entirely. Discrepancies are inevitable. Now real-world data that’s been gathered in large observational studies is attempting to close the gap between experimental, artificial study settings and clinical realities.