Weighted objectives method

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 This article is part of the Bachelor design guide; the original version can be found at page 182.


What is the weighted objectives method?

Figure 1: Example of the weighted objectives method (from student report).
Figure 1: Example of the weighted objectives method (from student report).

The weighted objectives method is an evaluation method for comparing design concepts based on an overall value per design concept. The biggest disadvantage of using the datum method or the Harris profile is that the scores per cri­terion cannot be aggregated into an overall score of the design alternative. This makes a direct comparison of the design alter­natives difficult. The Weighted Objectives Method does exactly this: it allows the scores of all criteria to be summed up into an overall value per design alternative.

The weigthed objective method assigns scores to the amount a design alternative satisfies a criterion. But the criteria used to evaluate the design alternatives with might differ in their importance. For example, the cost price can be of less importance than an appealing aesthetic. The weighted objectives method involves assigning weights to the different criteria. This allows the decision maker to take into account the difference in importance between criteria.

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When can you use the weighted objectives method?

The weighted objectives method is best used when a decision has to be made between a select number of design alternatives, design concepts or principle solutions. Usually, the weighted objectives methods is used when evaluating design concepts, and to make a decision which design concept should be developed into a detail design.

How to use the weighted objectives method?

Starting points

  • A limited number of concepts.

Expected outcome

  • A chosen concept.

Possible procedure

  1. Select the criteria with which the selection will be made. These criteria should be derived from the programm of requirements (note that probably not all requirements are applicable at this stage of the design process).
  2. Select 3 to 5 concepts for selection.
  3. Assign weights to the criteria. The criteria should be appointed weights according to their importance for the evaluation. To de­termine weight factor of the criteria it is recommended to compare the criteria pairwise to attribute a weight factor. Rank each of the the weights on a scale from 1 to 5 (you can also decide a total sum of the weights of the criteria, for example 100). Make sure to discuss the trade-offs between the criteria. Trade-offs will have to be made when weights are assigned to the individual criteria (determining which of the weights are more important).
  4. Construct a matrix, with the criteria as rows, and the concepts as collumns.
  5. Attribute values for each concept how it meets a criteria. Rank the score of the concepts from 1 to 10.
  6. Calculate the overall score of each concept by summing up the scores on each criteria (make sure to take into account the weight factor).
  7. The concept with the highest score is the preferred concept.

Tips and concerns

  • This method should be carried out intelligibly, discussing and reviewing both the weights assigned to the criteria and the scores of the concepts to all the criteria.

Literature

  • N. Roozenburg and E. Eekels (1995) Product Design: Fundamentals and Methods, Lemma, Utrecht.
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