What is a Random Variable?

Let's roll some dice

Usually, when we think of variables, they only tend to vary when we tell them to.

You might assign a value to a variable called HP (HP = 300) and then change it when the character takes 50 damage (HP = HP - 50) but the value at any given time is known. There’s no inherent uncertainty as to what the value is at any given time.

Random variables are different. We don’t know what their value is yet. Think about a six-sided die (D6) that hasn’t been rolled. We know what values it could take (1,2,3,4,5 or 6) but we don’t know what the end result is yet. The as-yet-unknown result of the D6 roll is still a variable we can work with, it’s just a random variable.

In fact, you’ll hear D&D players throw around random variables without thinking about it. When a player says that their spell does 3D6 damage on hit, what they’re really saying is “realise the value of the random variable “D6” three times and add the results together”.

If you google “3d6” now you can simulate this over and over again. But before you actually roll those three dice, you have to refer to their future value as… something and that ‘something’ is a random variable!

See you next time!