Datum method

From WikID

What Is a Datum Method?

Example of Datum Method (from student report)

The Datum Method is a method for evaluation of design alternatives. One of the alternatives is set as datum to which the other alternatives are compared for a range of criteria. Three judgements can be given: ‘worse’, ‘same’ or ‘better’ expressed in ‘–’, ‘0’ and ‘+’. The sum of each of these three values will then help to make a decision. The value of the alternatives is guessed on the basis of the ‘intuitive’ judgements of the decision-makers.

The method aims to provide the decision-makers with confidence through a systematic discussion of the criteria and by eliciting the advantages and disadvantages of the alternatives.

When Can You Use a Datum Method?

Whenever a number of alternatives of a product concept need to be compared to reach consensus in the evaluation or to make an intuitive decision, the Datum Method can be used. Although it can be used throughout the whole design process, commonly it is used to select concepts.

How to Use a Datum Method?

Howto-datum-method.png

Starting Point

Product concepts, developed to an equal, and thus comparable, level of detail.

A list of criteria suitable for use in this stage and in relation to the level of detail.

Expected Outcome

One or more strong concepts for further development, confidence in the decision for the chosen concept(s).

More understanding of the value of all the concepts, more insight in the problems still to be solved and a simple matrix to discuss with others and convince third parties.

Possible Procedure

  1. Arrange the concepts and criteria in a matrix (see figure 1).
  2. Choose one of the concepts as ‘datum’. Compare the other concepts to this datum and give a score for each criterium at the time (+ = better than datum, = worse than datum and s = similar/same).
  3. Indicate ∑ +, ∑ S and ∑ –.for each concept. Usually at least one concept will show more ‘–’ and less ‘+’. Usually a few concepts have minor differences. Discussion can start. An equal spread of pluses, minuses and similars indicates vague and ambiguous criteria.
  4. When the outcome does not distinguish enough, the process should be repeated until it does. Each time another concept should be taken as datum, leaving out the concept which was definitively worse.

Tips and Concerns

  • Sometimes the designer will not only totalise the score in ∑+, ∑ S and ∑ –, but also adds up the totals. Like each ‘+’ for one particular concept is compensated by each ‘-’ given to the same concept. A concept with two ‘+’, one ‘S’ and two ‘-’ will have an end score of zero (0). Although it is a way to have some outcome, one must realise that this will fade away the results and doesn’t help to discuss the concepts or criteria. Another concept might score zero (0) also, thus leading to the assumption that both concepts are equal, while the second concept initially scored one ‘+’, three ‘S’ and one ‘-’. It all depends on the weight of each criterion and the possibility to change a ‘-’ into ‘S’ or ‘+’ by redesign. The method is therefore not to be seen as a sort of mathematically justified process, but as an aid to the decision making.
  • Another aspect is the selection of criteria. Usually there are a lot of criteria to which the concepts do not comply to, yet. A criterion stating that the product should cost no more than 15 Euro’s, or weigh max 800 grams, cannot be judged in the early stages of the design process. However one may have some ideas about the relative difference in cost price. E.g. one concept seems to be more expensive than the other one, because of a larger number of parts or a more complex construction. In choosing the (more general reformulated criteria) it seems logical not to have more than eight to ten criteria.

References and Further Reading

  • Pugh, S. (1981) ‘Concept selection: a method that works’ In: Hubka, V. (ed.) Review of Design Methodology. Proceedings International Conference on Engineering Design, March 1981, Rome. Zürich: Heurista, 1981, pp.497 – 506.
  • Roozenburg, N.F.M. and Eekels,J. (1995) Product Design: Fundamentals and Methods, Utrecht: Lemma.
  • Roozenburg, N. and Eekels, J. (1998, 2nd ed.) Product Ontwerpen: Structuur en Methoden, Utrecht: Lemma.


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