Not all lines that fit best between a bunch of data points are straight. Rather, they could be curvilinear, just as you can have a curvilinear relationship between your variables, as we discussed in Chapter 5. For example, the relationship between anxiety and performance is such that when people are not at all anxious or very anxious, they don’t perform very well. But if they’re moderately anxious, then performance can be enhanced. The relationship between these two variables is curvilinear, and the prediction of Y from X takes that into account.
