I want to use mathematical construct to describe the relationship between our 5 fingers.

Since the thumb can move about with all the other fingers relatively still, we say the thumb is 100% independent.

We can almost say the same likewise for the 2nd and 3rd finger.

Ok...now the 4th finger can move about with slight disturbance to the 5th, say 10% influence on the 5th.

But the 5th finger has 90% influence on the 4th. if you move the 5th all the way down, the 4th goes along with it.

How should I describe this relationship between the 4th and 5th?

They have some kind of correlation, but its not symmetrical. How should we describe this kind of higher-order interaction?