Comprehensive Option Assesment - UNEP

Module 2: Comprehensive Options Assesment Stages
Scoring and rating of alternatives against each criterion
Each option is evaluated against each criterion. Because rating-and-weighting methods allow non-commensurate criteria to be used, these ratings
must be normalized on a standard scale, typically a 1- 100 scoring scale. Clearly, there is a considerable degree of judgment required in assigning
these ratings. Rather than seeing this as a weakness, this should be seen as an opportunity for the stakeholder groups to engage and discuss the pros
and cons of a particular design and to explore the implications of different ratings.
Each option is then assigned an overall score, obtained by multiplying the rating score of each criterion by the corresponding importance weight for
that criterion and then summing these weighted ratings for that option. This overall score describes how well the option meets all the criteria. The
options can then be arranged in order of their overall scores to give a preference ranking.
The preference ranking is usually highly dependent on the importance of the weights used, the choice of criteria, and the scaling method. Discussion
of the preference order of the options and what weights and ratings influenced the results will usually lead to changes in the weightings and ratings
and a recalculation of the preference order.
Because of its simplicity and transparency, rating-and-weighting is particularly useful for decision-making in the public domain. Rating-andweighting
approaches make choices and considerations explicit and facilitate discussions among stakeholders. In addition, they can be used at
various levels of decision-making. A group of farmers might use the method in order to establish their own preferences for different development
options, while a government agency responsible for sub-catchment management might use the method in order for strategic basin management
plans.
The rating-and-weighting process promotes transparency and communicates the values held by the different stakeholders. It gives a picture of what
different stakeholder groups deem to be important. The use of a wide range of criteria means that divergent views on the importance of one criterion
may not strongly affect the overall ranking of the option.
Obviously, assigning single rating values for each option against each criterion cannot fully replicate the complexity and subtlety of human decisionmaking.
In most cases, the stakeholder groups involved in the decision-making will not come to the process with a clear understanding of the
consequences of their choices. The decision-making process is necessarily one of exploration and learning, and the models and other methods of
determining the rating values should be seen as aids that inform a decision process. Consequently, the development of rating values is an iterative
process that evolves as the stakeholders refine their understanding of the consequences of each option.
Models can be used to measure the performance of individual options against criteria. Models can be complex or simple. As an example of complex
models, the downstream effects of options that change flow regimes and ecological functioning of the rivers are often assessed using a complex
hydrological model. Where ecological effects are expected, the hydrological model can be coupled to one or more ecological models of, for example,
wetland response to floods and ensuing changes in physical habitats.
The risks associated with the various options can be included as criteria. If not specifically included in the screening and ranking criteria, it is wise to
include a risk analysis as part of the assessment. Standard techniques include:
Comprehensive Options Assessment for sustainable development of infrastructure
Training Manual
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