Selection and valuation of criteria in decision-making ... - Trafikdage.dk

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Selection and valuation of criteria in decision-making ... - Trafikdage.dk

Selection and valuation of criteria in decision-making for improvements in

transport systems

v/Dag Bertelsen, SINTEF

This abstract does not, in fact, respond to the four key questions: background, methods,

results, conclusions. Nevertheless, it should give an good impression of the content in a

complete paper, which I hope will be of interest for the conference.

The aim of all decision-making, for companies as well as for the society as a whole, is to

choose the best among a number of alternative solutions. However, what is “the best” will

often depend on a judgement of the importance of different aspects of the alternatives.

Diversion in judgement among the decision-makers will lead to different conclusions as to

which solution is the best. On the other hand, lack of consistency and completeness in the set

of aspects included in the decision basis will normally lead to questionable decisions. Lack of

consciousness in the assessment of different aspects and solutions may also result in illogical

decisions.

For some decisions it is normal or acceptable to calculate and present all the relevant aspects

in a common monetary unit. This will be the case when comparing two different ways of

constructing a bridge. However, even then you have to ensure that all aspects are included and

no aspect is added more than once. If the reinforcement for a bridge is calculated as a separate

element, it is not to be included for each beam or pillar. If all principles for economic

calculations have been followed, the total costs will be a correct basis for decisions.

Often it is neither acceptable nor possible to calculate in monetary units all the aspects in

question, especially when health, environment and security aspects are involved. Then it will

be necessary to include into the decision process several aspects quantified in different units.

This results in a so-called multi-criteria decision-making.

It is much more challenging to secure a consistent decision basis for a multi-criteria situation

than for a single-criteria situation. Unfortunately, this is often disregarded both by the

decision-supporters and by the decision-makers.

A simple example of a multi-criteria decision situation exist when the number of injured

persons in different age groups is reduced by some improvements in the system in question,

for instance in the water supply system or in the transport system. Everyone realise that the

decision basis will be wrong if there are overlaps or gaps between the age groups when

presented for the decision-makers. This is as obvious as mistakes in calculation of

construction costs for a bridge. It is crucial for a rational decision that the decision basis

comprises a mutually consistent set of criteria.

Normally, the development of a consistent set of decision criteria will be quite more

complicated than illustrated above. Of course decomposition of benefits into subgroups has to

be consistent. It is quite more difficult to secure that the decision criteria is selected from the

same level in a cause-effect model for the system in question, especially in cases where no

formal cause-effect model is established. Then it is every reason to examine the criteria in the

decision basis before presenting them for the stakeholders and decision-makers. Without

some sort of a cause-effect model it will be almost impossible to secure a consistent set of

decision criteria. This has to be exemplified, here from the transport sector.


Persons

exposed

to noise

Persons

exposed to

pollution

Number of

traffic

accidents

Total

travel

time

Vehicle

operation

cost

Accident rate

Transport work

(vehicle*km)

Travel speed

Road length

Traffic volume

Road geometry

New link in the

transport system

Improvement of road

curvature

Expanding road width

Figure 1: The lower part of a simplified cause-effect model for improvements in a road

network

The red boxes at the top of figure 1 may be regarded as decision-criteria. The arrows represent

mathematical or other relationships between the various elements necessary to determine

quantities for each criterion. By using this model both for the existing and for the improved

transport system, the benefits can be calculated for various improvements.

Some people may consider accident rate, travel speed or road geometry as relevant decision

criteria in addition to, or instead of the criteria in the red boxes. Or they may consider health

impacts to be added to the red box criteria and presented for the decision-makers. How should

decision-supporters decide upon such questions?

Total life

quality for

everybody

Health

impacts

Consumption of

limited resources

Prosperity and

well-being

Persons

exposed

to noise

Persons

exposed to

pollution

Number of

traffic

accidents

Total

travel time

Vehicle

operation

cost

Figure 2: Idealised representation of the upper part of a cause-effect model

The decision-makers have to judge the relative importance of the decision criteria to come to

conclusions. Which considerations should it be rational for them to make in this connection?

They should be expected to have a superior aim and therefore an opinion on the contribution

of each criterion to this aim. In fact, this represents an upper part of the cause-effect model

shown in figure 2.


The upper part of the cause-effect model is significantly more dependent on personal opinions

than the lower part shown in figure 2. The purple box on the top raises the question weather

life quality for animal should be included, and even weather there is a life after death. These

are examples of aspects which politicians are supposed to take into account when making

their conclusions.

Noise as well as pollution and traffic accidents form, according to figure 2, the basis for

determination of health impacts. If health impacts from noise, pollution and accidents are

added to the red box decision criteria, then the decision-makers are invited to double count

these health aspects.

So, the red box criteria in figure 1 and 2 may be an appropriate set of decision-criteria for

situations covered by this cause-effect model. There will definitively also exist other sets of

decision-criteria which will satisfy the consistency requirements.

In figure 3 the whole rectangle

represents total benefits for a specific

decision situation. Each of the

coloured areas represents specific

decision criteria. In the left part of

the figure the total area is covered

and there is no overlap between any

of the criteria. In the right part there

are both overlap between many of

the criteria and parts of the area are

uncovered.

Figure 3: Illustration of one formally right and one wrong set of decision criteria

This is even more complicated since there will often exist a great variety of sets of decisioncriteria

which will not fulfil the consistency requirements. The decision-supporters are

expected to be aware of this and to avoid inconsistent sets of criteria in the decision basis.

Thus a main duty for decision-supporters is to select a set of criteria which give the

stakeholders and decision-makers a good basis for personal judgements and conclusions. It

must be admitted that this is not always paid the attention it should. In fact, the decisionsupporters

often ask the decision-makers to tell which set of criteria to be used, and then

regard this as a proper set of decision criteria.

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