Compensation method

The compensation method is the best-known variant and consists of attributing a weight to each criterion and then of calculating a global score for each measure, in the form of a weighted arithmetic average of the scores attributed to that measure for the different criteria. This variant is called "compensatory" because the calculation of the weighted average makes it possible to compensate between criteria. For example, a measure which had a very bad impact on the environment could still obtain a good global weighted score if its impact on employability were considered excellent.

Outranking method

The outranking variant is used where the criteria are not all considered commensurable, and therefore no global score can be produced. The analysis is based on multiple comparisons of the type: "does Measure A outrank Measure B from the point of view of the environment criterion?", "does Measure A outrank Measure B from the point of view of the employability criterion?", etc. These questions can be answered yes or no or be qualified, in which case the notions of a weak preference and a threshold criterion are introduced. The analysis makes all possible comparisons and presents a synthesis of the type: "Measure A is at least as good as Measure B, in relation to a majority of criteria (case of agreement), without being altogether too bad in relation to the other criteria (case of disagreement)".

The analysis could include protection against a favourable judgement for a measure that would be disastrous from the point of view of the given criterion, by setting a 'veto threshold' for each criterion. The introduction of a veto threshold strongly differentiates the logic of outranking from the logic of compensation. If there were a veto threshold, a very bad impact on the environment would make it impossible to consider the measure good, even if its impact on employability were considered excellent.

Outranking has the advantage of reflecting the nature of relations between public institutions better, since there is often a correspondence between evaluation criteria and evaluation stakeholders. In cases where the steering group is extended to about ten partners, it is not unusual for participants to identify themselves strongly with the "environment" or "employment" criteria. In this situation the outranking variant will probably better reflect the collective process of formulating a judgement within the steering group.