Repeat Order Rate = (COUNT DISTINCT(Order ID) WHERE Customer Order Count > 1 AND Dimension = xxx) / (COUNT DISTINCT(Order ID) WHERE Customer Order Count = > 1)

This relationship metric shows you the number of customers that have done the Parent and Child activity of all the customers that have done the Parent activity.

Let's say we are talking about the relationship between to products with the Parent being a shoe and the Child being a dress.

This metric will give you the percentage of people that have bought shoe that have also bought a dress.

So if 100 people bought a shoe and 65 of these also bought a dress, the percentage would be 65%