[sushiboat]

Prediction is not what you might think. Of course, I can't predict what a
modder is going to do. A modder could change Militia to be 10,000 gold. The
regression equations describe how stats are related to price for existing
units. To the extent that you generally like what Illwinter has done with
pricing units, the equations might give you a good starting point. If you want
to make drastic changes, you may be less interested.

My guess is that the Illwinter guys don't use equations. One of them probably
makes a unit and assigns a price based on an intuitive understanding of its
usefulness. After playtesting, the price is modified.

I can put things like magic paths and special abilities (e.g., ethereal) into the
mix. I already did so with flying, which turned out not to be uniquely
important enough to keep in. Keep in mind, however, that the equations
above are already explaining about 80% of the variance. That is the equivalent
of a correlation of .90. Whatever gains come in the future will be very modest
at best.

As for using nonlinear equations, I have looked at polynomial regressions for
some of the predictor variables. Morale, for example, is pretty much linear.
The squared term adds a little, and the cubed term is negligible. In other
contexts, I have played around with log, square root, and reciprocal
transformations. My experience has been that they are most useful when the
vanilla linear regression isn't working well. Here, vanilla works like
gangbusters, so the room for improvement is small.