A3.3 The weighted scoring method, also known as 'weighting and scoring', is a form of multi-attribute or multi-criterion analysis. It involves identification of all the non-monetary factors ("attributes" or "criteria" ) that are relevant to the project; the allocation of weights to each of them to reflect their relative importance; and the allocation of scores to each option to reflect how it performs in relation to each criterion. The result is a single weighted score for each option, which may be used to indicate and compare the overall performance of the options in non-monetary terms.
A3.4 This process necessarily assigns numeric values to judgements. These judgements should not be arbitrary or subjective, but should reflect expert views, and should be supported by objective information. To achieve meaningful results which decision-makers can rely on, it is important that:
(i) the exercise is not left to the 'experts', but is undertaken by a group of people who represent all of the interested parties, including, for example, those who are directly affected by the project, and those who are responsible for its delivery;
(ii) the group possesses the relevant knowledge and expertise required to make credible measurements and judgments of how the options will impact upon the criteria.
(iii) the group is led by an independent chairman to steer the process, probe opinions, promote consensus and avoid prejudice; and
(iv) the justification for the group's chosen weights and scores is fully explained.
A3.5 Appraisal reports should identify the personnel involved in the exercise, including an indication of their credentials, so that decision-makers are fully aware of whose views are represented. If there is a lack of consensus among members of the group regarding any of the weights or scores, the views of the dissenting individuals should be recorded.
A3.6 The process of deriving weights and scores is explained below step by step, covering the following stages:
1. Identify the relevant non-monetary criteria;
2. Weight the criteria to reflect their relative importance;
3. Score the options to reflect how each option performs against each criterion;
4. Calculate the weighted scores;
5. Test the results for robustness; and