PUGH CONCEPT SELECTION METHOD

INTRODUCTION:

Invented by Stuart Pugh the decision-matrix method, also Pugh method, Pugh Concept Selection is a quantitative technique used to rank the multidimensional options of an option set. It is frequently used in engineering for making design decisions but can also be used to rank investment options, vendor options, product options or any other set of multidimensional entities.

A basic decision matrix consists of establishing a set of criteria upon which the potential options can be decomposed, scored, and summed to gain a total score which can then be ranked. Importantly, the criteria are not weighted to allow a quick selection process.

The advantage of this approach to decision making is that subjective opinions about one alternative versus another can be made more objective. Another advantage of this method is that sensitivity studies can be performed. An example of this might be to see how much your opinion would have to change in order for a lower ranked alternative to out rank a competing alternative.

Concept Selection (Evaluation)

Concept selection is one of the most critical decision-making exercises in a product development. To make decisions effective, one must basically carry out two steps.

•Minimize the possibility of misrepresenting a solution that may be effective.

Engineer is not familiar with the technology.

•Fully consider the different ramifications of a decision.

For example, not considering the costumer’s need may lead to the product failing in the marketplace.

 

•Design Evaluations

Occurs at all phase of product evaluation, from concept to detailed design phases. Structured decision-making methods are needed.

•Quality of Information

Low quality of information- how well each alternative design would meet criterion cannot be fully understood.

High quality of information- the alternative solutions is well understood.

•Technology Readiness Assessment

If a technology is to be used as part of a product design, it must be mature enough that its use is a design issue, not a research issue.

•GO/NO-GO screening

Each concept must be compared to the customer requirements in an absolute fashion. Each customer need must be transformed into a question to be addressed to each concept. The questions should be answerable as either yes or maybe (go), or no (no-go).This evaluation will weed out concepts quickly and will help generate new ideas.

 

MECHANISM OF THE PUGH’S CONCEPT:

It is implemented by establishing an evaluation team, and setting up a matrix of evaluation criteria versus alternative embodiments. This is the scoring matrix usually associated with the QFD method and is a form of prioritization matrix. Usually, the options are scored relative to criteria using a symbolic approach (one symbol for better than, another for neutral, and another for worse than baseline). These get converted into scores and combined in the matrix to yield scores for each option.

1. Effective for comparing alternative concepts
2. Scores concepts relative to one another
3. Iterative evaluation method
4. Most effective if each member of a design team performs it independently and results are compared.

Comparison of the scores generated gives insight into the best alternatives.

CONCEPT SELECTION (PUGH’S METHOD)

Based on the Decision-Matrix (Pugh’s method), this method is very effective for comparing concepts that are not refined enough for direct comparison with the engineering requirements.

Figure 1

The method is an iterative evaluation that tests the completeness and understanding of requirements, quickly identifies the strongest concept.

The method is most effective if each member of the design team performs it independently. The results of the comparison will usually lead to repetition of the method, with iteration continued until the team reaches a consensus.

Step to Construct / Design Pugh Matrix

1.     Choose or develop the criteria for comparison.

1. Examine customer requirements to do this.
2. Generate a set of engineering requirements and targets.

2.      Select the Alternatives to be compared.

The alternatives are the different ideas developed during concept generation. All concepts should be compared at the same level of generalization and in similar language.

3.      Generate Scores.

       Usually designers will have a favorite design, by the time it comes to pick one. This concept   can be used as datum, with all the other being compared to it as measured by each of the customer requirements. If the problem is to redesign an existing product, then the existing product can be used as the datum.

      For each comparison the product should be evaluated as being better (+), the same (S), or   worse (-). Alternatively, if the matrix is developed with a spreadsheet like Excel, use +1, 0, and 1 for the ratings.

If it is impossible to make a comparison, more information should be developed.

4.      Compute the total score

1. Four scores will be generated, the number of plus scores, minus scores, the overall total and the weighted total.
2. The overall total is the number of plus scores- the number of minus scores.
3. The weighted total is the scores times their respective weighting factors, added up.
4. The totals should not be treated as absolute in the decision making process but as guidance only.
5. If the two top scores are very close or very similar, then they should be examined more closely to make a more informed decision.

5.      Variations on scoring

     A number of variations on scoring Pugh’s method exist. For example a seven level scale   could   be used for a finer scoring system where:

1. +3 meets criterion extremely better than datum
2. +2 meets criterion much better than datum
3. +1 meets criterion better than datum
4.   0  meets criterion as well as datum
5. -1  meets criterion not as well as datum
6. -2  meets criterion much worse then the datum
7. -3  meets criterion far worse than the datum

General Format for a Pugh Matrix:

    

		Concepts
Criterion	Wt	(Step 2)
(Step 1)	:	Generate score (step 3)
	:
:		:
:		:
Total +
Total -
Overall Total		Generate totals (step 4)
Weighted Total

                                               

 Example of Pugh Matrix

                                              Table 1.1 Handphone Selection

 

 

So how does this work? The basic steps of the Pugh Concept Selection Process are

1. Brainstorm alternatives; list them across columns of sheet. Make one alternative the “default” — often it’s the “do-nothing” or status quo choice. This choice is rated zero for all criteria.
2. Brainstorm criteria and characteristics important to the customer. List them down rows of sheet.
3. Begin filling in 1, 0, or -1 rating in the main area of sheet, based on whether that alternative is better, equivalent, or worse than the status quo for that criteria.
4. If some criteria are more important than others, adjust the weights. If some products are much better than others, adjust the rating weights in the main area of the sheet. Don’t go overboard with this.
5. Look at what the spreadsheet tells you the best choice. Do you and the group feel good about that decision? If so, we are done.
6. If not, look again at steps 1-5 — do you have a complete set of criteria, or was something important to the decision missed? Are the weights we have assigned close enough?

 

                                                       Table 1.2 Coffee Mill Design Conept

For the coffee maker, the best design is ‘Removable Blade” as its offer the max total of aggregate.

SUMMARY

a.       Estimation is a critical skill to develop and can help in quickly eliminating weak concepts

b.       •The feasibility of the concepts is based on the design team’s knowledge. It is often necessary to augment this knowledge with research and development of simple models.

c.        •In order for a technology to be used in a product, it must be ready.

d.       •A go/no-go screening based on customer needs helps to eliminate some of the concepts quickly.

e.        •The decision matrix (Pugh’s method) provides means of comparing and evaluating concepts. The method gives insight into strong and weak areas of the concepts.