Conclusion #1 is that software design is primarily about problem structuring.
Conclusion #2 is that the more structured the design problem was, the more the interview subject primarily discussed rational approaches to solve the problem, and the more that naturalistic approaches were facilitators to this discussion.
Conclusion #3 is that the less structured the design problem was, the more the interview subject primarily discussed naturalistic approaches to solving the design problem, and the more that rational approaches were facilitators to this discussion.
Conclusion#4 is that decision makers use either NDM or RDM as the dominant decision making approach but use aspects of the other decision making approach to implement their decision, depending upon the structure of the decision.
C. Zannier, M. Chiasson, F. Maurer
A Model of Design Decision Making based on Empirical Results of Interviews with Software Designers,
A Special Issue of the Journal of Information and Software Technology, p. 637–653, Feb 2007.