Fixed vs. Random Effects

My first exposure to random effects was in a Design of Experiments course, and to say I was confused would be an understatement. We dived right into deriving the equations for expected mean squares, and yet I felt like I didn’t really understand why or when a variable should be treated as a random vs. a fixed effect. So I created a simple app that attempts to give a more intuitive explanation of the difference between fixed and random effects: Random Effects App