In this figure, a model is considered to have fewer side effects when the ER is smaller at the same RER (i.e., smaller value of y for a fixed value of x), or when the RER is larger at the same ER (i.e., larger value of x at the fixed y).
the closer a model is plotted to the corner B of the graph, the better the model is; the closer it is to the corner A, the worse the model is.