Figure 8-3 An example design trade matrix for three concepts and three weighted criteria.
- Poor requirements definition can result in a trade result that may not be good for properly defined requirements.
- Valuable alternatives may be missing if alternatives are defined without brainstorming by several experienced people with a diversity of skills and experience.
- Allowing biased weightings or selection criteria often results in selecting alternatives that are driven by the biases and not the optimum alternative that would be selected with unbiased trades.
- The fatal error is having no winner. This results if the spread of the weighted score is less than the spread of estimates of errors. The sensitivity analysis step in Figure 7.1 is crucial to effective trades.
- Inappropriate models used for determining attribute scores. Models not only have to be relevant to the trade being performed they must have credibility in the eyes of the decision makers, they should lead to scores for the different alternatives that are spread more than the estimates of errors in the model results, the algorithms and internal mathematics must be transparent to the users and they must be sufficiently user friendly that the analysis can be conducted with confidence and in a timely manner.
- Conducting system and design related trade studies outside the control of systems and design engineering. Development program managers sometimes pull systems and design engineers off programs early to save money and then allow procurement, operations or product assurance personnel to conduct trades without the oversight of the appropriate systems or design engineers. This can lead to a multitude of difficulties and usually expensive difficulties. Suffice it to say that systems engineers and design engineers must retain control of systems and design trades throughout the life cycle.