Ridge Analysis 25 Years Later

The response surface technique called ridge analysis was originally introduced by Hoerl (1959) more than 25 years ago. Despite tremendous advantages over more conventional response surface procedures when more than two independent variables are present, ridge analysis has received little attention in the statistical literature since then, although numerous applications have appeared in engineering journals. This situation may be partially due to the fact that this procedure led to the discovery of ridge regression, which has completely overshadowed ridge analysis in the literature since. This discussion will briefly review the mathematics of ridge analysis, its literature, practical advantages, and relationship to ridge regression.