# Confounder A confounder is a causal variable C that causes both A and B, which makes A and B look correlated even though they don’t have a causal relationship. <!-- #mental-model --> [Web URL for this note](http://notes.benjaminreinhardt.com/Confounder) [Comment on this note](http://via.hypothes.is/http://notes.benjaminreinhardt.com/Confounder) <!-- {BearID:9E4E8E5D-121F-48BC-B43B-6CD47BED6455-45759-00016185BB7F7A1E} -->