Economic evaluation of road safety measures - Swov

5.5.2. Multi-criteria methods
Once the effects overview has been drawn up, the ranking per criterion of
each alternative can be indicated by means of a number (as in the
example) or a colour. The entire overview then takes on the appearance of
a scorecard. The assessment of the relative importance of the scores (the
'weight') is a matter for those who have to make the final selection.
Both the costs and effects of each alternative can be spread over time in
different ways. It therefore becomes necessary to apply a correction for
each criterion, wherever possible. The discounting method can be used for
all scores expressed in monetary terms. Where this method is not
appropriate, the effects can be aggregated over the entire lifetime, or
expressed as an annual average. The scorecard should be accompanied by
an explanation of the manner in which the scores and their ranking have
been arrived at.
This class of evaluation methods is characterized by the fact that they rely
on various explicit assessment criteria. These can differ significantly. The
relevant scores per criterion can each be expressed in an appropriate unit
and can not therefore be aggregated over the criteria. A second important
characteristic of multi-criteria methods is that greater importance is
attached to some criteria than to others in making the overall assessment.
This is achieved by assigning each a 'weight' that should reflect the
preferences of the decision-maker(s). Where there is a significant
divergence of opinion between the decision-makers, several sets of
weighting factors may be used. Like the effects themselves, the weights
may be expressed quantitatively or qualitatively. The exact form they take
will depend on the method used.
There are many multi-criteria methods, including the weighted aggregation
method, the goals achievement matrix, the concordance analyse, the
permutation method, the regime method, the multi-dimensional scale
analysis and the Evamix approach. Here, it will be sufficient for us to
confine our attention to just one example, the goals achievement matrix
(GAM) method.
The GAM method relies on the principle of bringing the effects of the
various alternatives into relationship with a number of stated social
objectives. For each objective, a so-called 'cost-benefit account' is created,
showing the degree to which that particular objective is achieved. Here, the
costs and returns are defined somewhat differently than in the CBA: the
effects are expressed as negative changes (costs) and positive changes
(benefits) with regard to desired situation. In Table 5, an example of a
relatively simple GAM is presented, showing just one alternative, two
objectives and five groups of interested parties.
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