What is the difference between perfect and imperfect mutlicolinearity?

Question

What is the difference between perfect and imperfect mutlicolinearity?

In: Mathematics

Answer 1

Your identical twin is perfectly collinear with you. Your other siblings are all imperfectly collinear with you.

I can predict a lot about what you look like by looking at your siblings. But I can predict exactly what you look like by looking at your identical twin.