ELECTRE

ELECTRE refers to a family of multi-criteria decision analysis (MCDA) methods designed to assist decisions where several conflicting criteria must be considered. Originating in France in the 1960s and 1970s, the ELECTRE family was developed by Bernard Roy and his collaborators. The methods share an outranking approach, where alternatives are compared pairwise and a dominance relation is derived rather than relying solely on aggregate scores.

The core idea is pairwise comparison using concordance and discordance indices. For each pair of alternatives, concordance reflects the weight of criteria favoring A over B; discordance reflects the strength of criteria opposing it. A credibility score combines these elements, and A outranks B if this credibility exceeds a threshold.

The ELECTRE family includes ELECTRE I, II, III, and IV, as well as ELECTRE TRI for sorting into predefined categories. ELECTRE I uses a simple outranking relation; ELECTRE II and III introduce more elaborate ranking and threshold handling; ELECTRE IV focuses on robustness under uncertainty. ELECTRE TRI assigns alternatives to categories with vetoes and category thresholds, enabling a categorical classification rather than a pure ranking.

The typical workflow involves defining criteria and weights, normalizing data, computing concordance and discordance, and applying thresholds to form the outranking relation. The decision output may be a complete or partial ranking, or an assignment to categories via ELECTRE TRI.

Applications are found in environmental planning, energy and transport policy, finance, and product design. Strengths include handling diverse and conflicting criteria, and working with uncertainty and qualitative judgments. Limitations include sensitivity to the choice of weights and thresholds and potential computational complexity for large problems.