Decision Methods
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Transcript of Decision Methods
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DECISION METHODS FOR EVALUATION
OF ALTERNATIVES
Environmental impact studies typically address a minimum of
two alternatives, and sometimes as many as ten, but usually
three to five alternatives
Typical categories of alternatives, expressed generically,
include
Site location alternatives
Design alternatives for a site
Construction, operation, and decommissioning alternatives for a
design Project size alternatives
Phasing alternatives for size groupings
No-project or no-action alternatives
Timing alternatives relative to project construction, operation,and
decommissioning
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Conceptual Basis for Tradeoff
Analysis Tradeoff analysis involves the comparison of a set of alternatives
relative to a series of decision factors.
The following approaches can be used to complete the tradeoffmatrix
Qualitative approach: Descriptive, synthesized, and integrated
information on each alternative relative to each decision factoris presented in the matrix.
Quantitative approach: Quantitative, synthesized, andintegrated information on each alternative relative to eachdecision factor is displayed in the matrix.
Ranking, rating, or scaling approach: The qualitative orquantitative information on each alternative is summarized viathe assignment of a rank, rating, or scale value relative to eachdecision factor (the rank or rating or scale value is presented inthe matrix).
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Weighting approach: The importance weight of eachdecision factor relative to each other decision factor
is considered, with the resultant discussion of theinformation on each alternative (qualitative;quantitative; or ranking, rating, or scaling) beingpresented in view of the relative importance of thedecision factors.
Weighting-ranking, -rating, or -scaling approach:The importance weight for each decision factor ismultiplied by the ranking, rating, or scaling of eachalternative, then the resulting products for each
alternative are summed to develop an overallcomposite index or score for each alternative; theindex may take the form of:
Index j = (IW)i (R)ij
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TRADEOFF ANALYSIS FOR DECISION MAKING (CANTER,ATKINSON, AND LEISTRITZ 1985)
Alternatives
Decision Factors 1 2 3 4 5
Degree of Meeting Needs
and Objectives
Economic Efficiency
Social Concerns
(public preference)
Environmental Impacts
Biophysical
Cultural
Socioeconomic
(includes health)
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Importance weighting for decision
factors
EXAMPLES OF IMPORTANCE WEIGHTING TECHNIQUES USED INENVIRONMENTAL STUDIES
Ranking
Nominal group process
Rating
Predefined importance scale
Multiattribute utility measurement
Unranked paired comparison
Ranked paired comparison
Delphi
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Ranking techniques for importance weighting
basically involve the rank ordering of decision
factors in order of importance. If n decision
factors exist, rank ordering involves assigning
1 to the most important factor, 2 to the
second-most important factor, and so forth,until n is assigned to the least important
factor. The rank order numbers can be
reversed.
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The Nominal Group Process (NGP) technique
(Voelker 1977) illustrates a ranking technique
The NGP technique is widely used in health,
social service, education, industry, and
government organizations.
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Rating techniques for importance weightingbasically involve assigning importancenumbers to decision factors and sometimes
their subsequent normalization via amathematical procedure.
Predefined importance scale(Linstone and
Turoff 1978) Multi-attribute utility measurement(MAUM)
technique (Edwards 1976)
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Predefined importance scales
Decision factors can be assigned numerical
values based on predefined importance scales
Use of the predefined scales can aid in
systematizing importance weight assignments
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Scale Reference Definitions
1. Very important A most relevant point
First order priority
Has direct bearing on major issues
Must be resolved, dealt with, or treated
2. Important Is relevant to the issue
Second order priority
Significant impact, but not until other
items are treated
Does not have to be fully resolved
3. Moderately important May be relevant to the issue
Third order priority
May have impact
May be a determining factor to major issue
4. Unimportant Insignificantly relevant
Low priority
Has little impact
Not a determining factor to major issue
5. Most unimportant No priority
No relevance
No measurable effectShould be dropped as an item to consider
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Multi-attribute utility measurement
(MAUM)
Can be used by an individual, a small group of
persons or multiple publics. Ten basic steps in
the MAUM technique are described follows:
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Step 1 Identify the person or organisation whose utilities are to be maximized
Step 2 Identify the issues to which the utilities needed are relevant
Step 3 Identify entities to be evaluated. They are outcomes of possible actions. But in a
sense, the distinction between an outcome and opportunity for further actions isusually fictitious.
Step 4 Identify the relevant dimensions of value for evaluation of the entities. It is
important not to be too expansive at this stage. The no:of relevant dimensions of
value should be modest, for reasons the will be apparent shortly.
Step 5 Rank the dimension in order of importance. The ranking can be done by
individual, by an interdisciplinary study team by representatives of parties having
conflicting interest acting separately or as a group.
Step 6 Rate the dimensions in terms of importance, preserving existing ratios. The
respondents will need to review previous judgments to make them consistent
with present ones.
Step 7 Sum the importance weights, divide each by the sum and multiply by 100.
Step 8 Measure the location for each entity being evaluated on dimensional yard stick
Step 9 Calculate utilities for entities .
Step 10 Decide if a single alternative is to be chosen.
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Paired comparison techniques (unranked andranked)for importance weighting involve
comparisons between decision factors and asystematic tabulation of the numerical results ofthe comparisons.
These techniques are used extensively in decision-
making efforts, including numerous examplesrelated to environmental impact studies.
Can be used by an individual or group, compareseach decision factor to each other decision factor in
a systematic manner.
If there are four basic decision factors F1 to F4, theuse of above technique is show below
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Factor Assignment of weight Sum FIC
F1 1 1 1 1 4 0.4
F2 0 1 0 1 2 0.2
F3 0 0 0 1 1 0.1
F4 0 1 1 1 3 0.3
F5 (Dummy) 0 0 0 0 0 0
10 1.0
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Scaling, Rating, or Ranking of
Alternatives
Scaling, rating, or ranking of each alternative foreach decision factor is the second major aspect inusing the multicriteria decision-making approach.
Examples of techniques include the use of thealternative profile concept, a referencealternative, linear scaling based on the maximumchange, letter or number assignments
designating impact categories, evaluationguidelines, unranked paired comparisontechniques, and functional curves.
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Alternative profile concept
for impact scaling
This concept is represented by a graphic presentationof the effects of each alternative relative to eachdecision factor.
Each profile scale is expressed on a percentage basis,ranging from a negative to a positive 100%, with 100%being the maximum absolute value of the impactmeasure adopted for each decision factor
If the decision factors are displayed along with the
impact scale from -100% to +100%, a dotted line canbe used to connect the plotted points for eachalternative and thus describe its profile.
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Scaling technique in which the actual measures ofthe decision factor for each alternative plan arenormalized and expressed as a decimal of thelargest measure for that factor. This techniquerepresents linear scaling based on the maximumchange
Letter scaling system incorporates eightyenvironmental factors oriented to the types ofprojects conducted by the U.S. Department ofHousing and Urban Development. The scaling
system assigns a letter grade from A1 to C2 for theimpacts, with A1 representing a major beneficialimpact and C2 an undesirable detrimental change
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Scalingfollows establishing an evaluation
guideline for each environmental factor. An
evaluation guideline is defined as the smallestchange in the highest existing quality in the
region that is considered significant
Functional curves, also called value functionsand parameter function graphs or curves, can
also be used in environmental impact studies for
scaling, rating, or ranking the impacts of
alternatives relative to decision factors.
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Decision-Focused Checklists
The Battelle Environmental Evaluation System
(EES) is a weighting-scaling checklist
developed for the U.S. Bureau of Reclamation.
It contains seventy-eight environmental
factors organized into seventeen components
and four categories as shown
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Another example of a weighting-scaling checklist for water resources projects is the Water
Resources Assessment Methodology (WRAM) developed by the U.S. Army Corps of Engineers
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Current Trends in Decision-Making
Tools
A recent trend in decision making in environmental
studies is the use of computer software. For example,
Torno et al. (1988) developed a training manual to
evaluate the environmental impacts of large-scalewater resources development projects.
A decision-support system computer model, called d-
SSYS, can help determine the relative weights ofevaluation parameters used to evaluate projects and
the utility function for each of the attributes