evaluating concepts_weighted objectives

Evaluating Alternatives

concepts evaluation methods

ConceptC

Concept A

Concept B ???

• the designer is then faced with the problem of selecting the best concept. • decisions of choice to be made between alternative sub-solutions or alternative features that might be incorporated into a final design. • choosing between alternatives is therefore a common feature of design activity.

Evaluating Alternatives...(2)Selecting a ‘best’ concept can be done by;

intuition, experience, arbitrary decision.

Needs some more rational, or at least open, procedure. more secure in making the choice, consensus decision involving clients, managers

and colleagues in the design team, able to participate in or assess the validity of

the choice.concepts evaluation methods

not secure, prone to making errors.

Evaluating Alternatives...(3)How to begin?

Get information from design process used earlier on; criteria established by the performance specification

method; design objectives established by the objectives tree

method. An evaluation of alternatives can only be done by

considering the objectives that the design is supposed to achieve.

An evaluation assesses the overall value/utility of a particular design proposal with respect to the design objectives. different objectives have different perceived values, entails some means of differentially weighting

objectives.


Evaluating Alternatives...(4)Weighted objectives method is

the right technique to assess and compare alternative designs, using differentially-weighted objectives.

This method assigns numerical weights to objectives, and numerical scores to the performances of alternative designs measured against these objectives. Needs design objectives that are

measurable; Interval/ratio data!


O1

O11

O111 O112

O12

O113

An objective tree functions

The Weighted Objectives MethodSteps:


1

•List the design objectives

2

•Rank order the list of objectives

3

•Assign relative weightings to the objectives

4

•Establish performance parameters or utility scores for each of the objectives

5

•Calculate and compare the relative utility values of the alternative designs

List the design objectives


An evaluation of the design objectives is based on to a set of criteria,objectives should be established at an early of the

design process. however, at the later stages of the process, they

may be modified/discarded/changed,Types of design objectives;

technical, economic , factors, user requirements, safety requirements...etc each with their own merits.

some are quantitative and some are qualitative. the qualitative objectives need to be scored on a range of

scales.

Draw a comprehensive listing of design objects that have been established.

Don’t miss out anything!

Rank order the list of objectives


The list of objectives contains a wide variety of design requirements,

ranged from least to most critical/important. Determine their relative weights;

list them in a rank order of importance.

Pair wise comparison

Most important

Least important

Assign relative weightings to the objectives

Assign a numerical value to each objective, representing its weight relative to the other objectives.


a) positions of relative

importance, or value,

on a scale (1 to 10 or 1 to 100)

b) Points awarding based on 100 points

c) Use of an objectives tree for assigning

relative weights to sub-objectives

low consistency, validity - - - - - - - - - - - - - - - - - - - - - - highconsistency, validity

Relative importance/value based on a scale (1 to 10 or 1 to 100)


The most important objective, B, has been given the value 10, and the others are then given values relative to this. Thus, objective C is valued as about 70% of the value of objective B; objective A is valued twice as highly as objective E; etc. The corresponding scale values are the relative weights of the objectives.

Points awarding based on 100 points


Allocate a certain number of points,

(e.g.,100) among all the objectives

~ awarding points on relative value.

~ making trade-offs and adjustments between the

points awarded to different objectives until acceptable

relative allocations are achieved.

Use of an objectives tree for assigning relative weights to sub-objectives


An objectives tree provides a more reliable method of

assigning weights

~ The highest-level overall objective is given the value 1.0; ~ at each lower level the sub-objectives are then given weights relative to each other but which also total 1.0.

‘true' weights are calculated as a fraction

of the 'true' weight of the objective above them.

Use of an objectives tree for assigning relative weights to sub-objectives...(2)


Relative weights

‘true’ weights: (.67 x .5) & (.33 x .5)

Establish performance parameters/utility scores for each of the objectives


Design objectives have 2 categories:

Quantitative design parameters

Qualitative design parameters

~ interval data, measurable.e.g., engine fuel consumption of 10km/liter.

~ assign utility scores estimated on a points scale

scale performance

1 far below average

2 below average

3 average

4 above average

5 far above average

Quantitative vs. Qualitative measurements


Range of point scales


Calculate and compare the relative utility values of the alternative designs

1. Calculate a score for each one’s performance on the established parameters.

must involve participation of all members of the design team,

different solutions may be scored differently by different people.

2. Add up the utility value scores for each alternative.

3. Based on the overall total scores, rank the alternatives in the proper order (i.e., from best to worst)

the best overall utility value may be highly misleading; needs more discussions, decisions, rankings and

comparisons to select the ‘best’ concept.


Example : Reusable syringe


Initial evaluation for seven concepts

Example : Reusable syringe...(2)


Final evaluation for selected, combined and refined concepts

Example : Reusable syringe...(3)


Concept D

Concept F

Combined concept DF

Example : Bicycle splashguard


Initially, concept II emerged as the clear leaderConcept II wasselected as a new datum and comparisons made with concepts IVand V.

Concept II was confirmed to be the ‘best’ alternative.

evaluating concepts_weighted objectives

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