Principal points are cluster means for theoretical distributions. A discriminant methodology based on principal points is introduced. The principal point classification method is useful in clinical trials where the goal is to distinguish and differentiate between different treatment effects. Particularly, in psychiatric Studies where placebo response rates can be very high, the principal point classification is illustrated to distinguish specific drug responders from nonspecific placebo responders. (C) 2009 Elsevier B.V. All rights reserved.