How do I affect variables at random?

Hey there! I'm trying to set up my game. I have a character that has four different stats, and what I want is for the system to pick a random one every ten seconds and affect its value. So essentially, this is what I want:

System > Pick a variable from the list at random to affect > Subtract from that value

Is there a way to do this?

What if you generated a random number from 1 to 4 and if it’s 1 change the first variable, or if it’s 2 the second, and so on.