Evaluating Design Alternatives. - PowerPoint PPT Presentation

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Evaluating Design Alternatives.

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The attached narrated power point presentation explores the method of choosing the best design alternative among a set of available alternatives. – PowerPoint PPT presentation

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Date added: 10 December 2024
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Title: Evaluating Design Alternatives.


1
EST 200, Evaluating Design Alternatives
  • MEC

2
Contents
  • Decision Making.
  • Choosing the Best Alternative.
  • Numerical Evaluation Matrix.
  • Priority Checkmark Method.
  • Best-of-Class Chart.
  • Design Evaluation.

3
Decision Making
  • A selection process.
  • The best or most suitable course of action
    finalized from among several available
    alternatives.
  • Intellectual and Goal Oriented.
  • Involves imagination, reasoning, evaluation and
    judgement.
  • Involves commitment of resources.

4
Effectiveness of decision making enhanced by
participation.
5
  • Our job is to give the client, on time and on
    cost, not what he wants, but what he never
    dreamed he wanted and when he gets it, he
    recognises it as something he wanted all the
    time
  • - Sir. Denys
    Louis Lasdun,
  • Architect.

6
Choosing the Best Alternative
  • Resources are limited eg time, money, expertise
    etc.
  • Rarely are the resources available to fully
    develop more than one design scheme.
  • Never mind all of our alternatives.
  • Must choose the best alternative for further
    elaboration, testing, and evaluation.

7
Choosing the Best Alternative
  • Limit the analysis to the clients most important
    objectives.
  • Avoid drowning useful information in a sea of
    relatively unimportant data.
  • Establish metrics with common sense of scale.
  • Do not mistakenly over/underemphasize some
    results.

8
Choosing the Best Alternative
  • Information must necessarily reflect a fair
    amount of subjectivity.
  • Many of the metrics reflect qualitativenot
    measurable, quantitativeresults.
  • Metrics should be thought of more as indicating a
    clear sense of direction than an algorithm or
    numerical solution.

9
Choosing the Best Alternative
  • Check that each alternative satisfies all of the
    applicable constraints.
  • Design alternatives that dont meet constraints
    considered infeasible.
  • Three selection methods to link design
    alternatives to ordered unweighted design
    objectives.

10
Pareto Optimality
  • Named after Vilfredo Pareto.
  • Pareto improvement Resources can be re-allocated
    to make at least one person better off without
    making other individuals worse off.
  • Pareto optimal/Pareto efficient Situation where
    no individual/preference criterion can be better
    off without making at least one
    individual/preference criterion worse off or
    without any loss thereof, means no scope for
    further Pareto improvement.

11
A, B - Pareto inefficient , Pareto improvement
since total output increases. C,D Pareto
Efficient, No improvement possible.
Upper Limit
12
Pareto Efficiency
  • Implies resource allocation in the most
    economically efficient manner.
  • Does not imply equality or fairness.
  • Resources cannot be reallocated to make one
    individual better off without making at least one
    individual worse off.
  • Economy in a Pareto optimum state when no
    economic changes can make one individual better
    off without making at least one other individual
    worse off.

13
Methods of Choosing an Alternative
  • Three selection methods
  • - numerical evaluation matrix.
  • - priority checkmark method.
  • - best of class chart.
  • Ordered objectives cannot be scaled on a
    mathematically meaningful ruler.
  • May bring order to judgments and assessments that
    are subjective at their root.

14
Numerical Evaluation Matrix
  • Constraints (upper rows) and objectives (lower
    rows) in the left-hand column.
  • Limit the number of decisive objectives to the
    top two or three.
  • Difficult to mediate among more than two or three
    objectives at one time.
  • Reflects the application of the metrics to the
    design alternatives.
  • To see if one design is Pareto optimal - superior
    in one or more dimensions, and at least equal in
    all the others.

15
Numerical Evaluation Matrix
  • Values can be used to work with the client (and
    perhaps users) to revisit the objectives.
  • Client may change their mind about relative
    rankings to get a very strong winner.
  • Metrics and associated testing procedures not to
    change with whoever is applying or making
    measurements for the metrics.

16
Numerical Evaluation Matrix- Juice Container
Design
17
Priority Checkmark Method
  • A simpler, qualitative version of the numerical
    evaluation matrix.
  • Easy to use, makes the setting of priorities
    simple, readily understood by clients and other
    parties.
  • Ranks the objectives as high, medium, or low in
    priority.
  • However, considerable information is lost that
    may be useful in differentiating between
    relatively close alternatives.

18
Priority Checkmark Method
  • Objectives with high priority given three checks,
    those with medium priority given two checks,
    objectives with low priority given only one
    check.
  • Design alternative that meets an objective in a
    satisfactory way marked with one or more checks.

19
Priority Checkmark Method
  • Metric results assigned as 1 if they are awarded
    more than the target value (eg 70 points on a
    0100 scale), and as 0 if their award is less
    than the target value.
  • Choice of a target value (threshold) very
    important.
  • May lead to results that appear to be more
    disparate than they really are.

20
Priority Checkmark Method - Juice Container
Design
21
Best-of-Class Chart
  • For each objective, assign scores to each design
    alternative.
  • 1 for the alternative that meets that objective
    best, 2 for second-best and so on..
  • Alternative that met the objective worst given a
    score equal to the number of alternatives being
    considered.

22
Best-of-Class Chart
  • Two alternatives can be considered best,
    handled by splitting available rankings.
  • Eg two firsts would each get a score of
    (12)/2 1.5, second and third would get
    (23)/2 2.5.
  • Scores help to see if the design is Pareto
    optimal (best in all categories), or at least
    best in the most important (i.e., highest ranked)
    objectives.

23
Best-of-Class Chart- Juice Container Design
24
Best-of-Class Chart - Merits
  • Allows us to evaluate alternatives with respect
    to the results for each metric.
  • No binary yes/no decisions.
  • Easy to implement and explain.
  • Ranking methods allow for qualitative evaluations
    and judgments.
  • Can be done by individual team members or by a
    design team as a whole.

25
Best-of-Class Chart - Merits
  • Helpful if there are many alternatives to choose
    among from.
  • Can be used if we want to narrow our consultative
    and thoughtful process to the top few.

26
Best-of-Class Chart - Drawbacks
  • Encourages evaluation based on opinion rather
    than testing or actual metrics.
  • Shows only the rankings, not the actual score.
  • May lead to a moral hazard akin to that attached
    to priority checkmarks.
  • Temptation to fudge the results or cook the books.

27
Best-of-Class Chart - Drawbacks
  • May not provide information on whether two
    results are close or not.
  • Eg we do not know if the first and second
    results are close or not, which could be
    important information.

28
Design Evaluation
  • Design evaluation and selection demand careful,
    thoughtful judgment.
  • Ordinal rankings of the objectives obtained using
    PCCs cannot be meaningfully scaled or weighted.
  • Cannot simply sum the results.
  • Use common sense when evaluating results.

29
Design Evaluation
  • Metrics results for two alternative designs that
    are relatively close to be treated as effectively
    equal, unless there are other unevaluated
    strengths or weaknesses.
  • Results should meet the expectations.
  • No excuse for accepting results blindly and
    uncritically.

30
Design Evaluation
  • If results do meet our expectations, ask whether
    evaluation was done fairly.
  • Should not reinforce biases/preconceived ideas.
  • Check whether the constraints used to eliminate
    designs are truly binding.

31
Thank You
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