Tukey (1977) describes an orderly technique for re-expressing variables employing a power transformation. You may well be familiar with polynomial regression (a form of multiple regression) by which the simple linear model y = b0 + b1X is extended with terms such as b2X2 + b3X3 + b4X4. Alternatively, Tukey http://menachemy358iui6.slypage.com/profile