The second approach used for establishing internal validity was reviewing the research results with a subset of the same designers as well as a small group of outside designers. Six validation interviews were performed _three from the original group of interviewees and three outside designers_ to confirm the determinants of evolution and sensitivity. With a few exceptions, the interviewees were able to easily visualize how each of the determinants affected evolution or sensitivity, and in some cases, were able to provide examples from their work experiences. The hardest determinants for the interviewees to visualize were input sensitivity, integration sensitivity, and constraint satisfaction for evolution. Some interviewees required further definition and examples to accept these results.