Overview of Methodology
We present a two-stage concept selection methodology, although the first stage may suffice for simple design decisions. The first stage is called concept screening and the second stage is called concept scoring. Each is supported by a decision matrix that is used by the team to rate, rank, and select the best concept(s). Although the method is struchtred, we emphasize the role of group insight to improve and combine concepts.
Concept selection is often performed in two stages as a way to manage the complexity of evaluating dozens of product concepts. The application of these two methods is illustrated in Exhibit 8-4. Screening is a quick, approximate evaluation aimed at producing a few viable alternatives. Scoring is a more careful analysis of these relatively few concepts in order to choose the single concept most likely to lead to product success.
During concept screening, rough initial concepts are evaluated relative to a common reference concept using the screening matrix. At this preliminary stage, detailed quantita tive comparisons are difficult to obtain and may be misleading, so a coarse comparative rating system is used. After some alternatives are eliminated, the team may choose to move on to concept scoring and conduct more detailed analyses and finer quantitative evaluation of the remaining concepts using the scoring matrix as a guide. Throughout the screening and scoring process, several iterations may be performed, with new alternatives arising from the combination of the features of several concepts. Exhibits 8-5 and 8-7 illustrate the screening and scoring matrices, using the selection criteria and concepts from the syringe example.
Both stages, concept screening and concept scoring, follow a six-step process that leads the team through the concept selection activity. The steps are:
I. Prepare the selection matrix.
2. Rate the concepts.
3. Rank the concepts.
4. Combine and improve the concepts.
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When available, objective metrics can be used as the basis for rating a concept. For example, a good approximation of assembly cost is the number of parts in a design. Similarly, a good approximation of ease of use is the number of operations required to use the device. Such metrics help to minimize the subjective nature of the rating process. Some objective metrics suitable for concept selection may arise from the process of establishing target specifications for the product. (See Chapter 6, Product Specifications, for a discussion of metrics.) Absent objective metrics, ratings are established by team consensus, although secret ballot or other methods may also be useful. At this point the team may also wish to note which selection criteria need further investigation and analysis.