Is understanding propensity scores a headache for you? Join the crowd! You've heard of crowd-sourcing, this is crowd-sorting. Imagine you are in a crowd of 216 people who have packed a lecture theatre for a day-long course on managing migraines. Dr. Maclure guides us through a pictorial explanation of how the people in the theatre can be sorted into groups based on confounding variables such as drinking coffee and smoking. He then shows how to balance the different groups by matching. This is a very concrete and visual example of how propensity scores can be used in observational studies.