I also agree that both are at best only approximations to actual lifetime incomes. Fortunately some of the errors in such an approximation may disappear since the same types of biases are apt to appear in both W and W*, and onlv the ratio of W to W* is used in the analysis. I find the Motley-Morley method of calculating optimum life-time incomes interesting, but I am puzzled as to why their model becomes the Thurow technique when it yields incorrect results. They show that equation (7) yields a convex path when the normal income path is concave and the true optimal path is postulated as constant. I agree with the conclusions, but equation (7) is not the estimating equation which I used. It is even labelled an alternative model. Thus, I can hardly consider the incorrect results a critique of my estimating equation. A Growth Model of International Direct Investment