e.g. W.F. Massy (1965), Principal Component Regression in Exploratory Statistical Research, Journal of the American Statistical Association, 60, 234-246

e.g. Martens, H., Wold, S., and Martens, M. (1983), a laymans guide to multivariate data analysis. In Food Research and Data Analysis, H. Martens and H. Russworm, Jr. (eds) 473-492. London : Applied Science Publications

e.g. Hoerl, A.E.and Kennard, R.W. (1970), Ridge regression biased estimation for nonorthogonal problems, Technometrics, 8, 27-51