On validating design decision methodologies

In this paper an argument for validation of design decision methods is presented. In the process of justifying the need for validation, the elements of what a valid design methodology is are derived and a formal definition is presented. Under this definition, critical evaluation of two popular decision support methods, the House of Quality and Suh's Axiomatic Design, is presented using a simple design problem and both are shown to be flawed under the proposed definition of validity. This does not imply that the methods are ineffective. In fact, under the appropriate assumptions, they are quite useful. However, in this paper, an investigation of the validity of these assumptions is conducted, including a more general definition of validity with respect to decision support methods in design.