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The paper opens the debate on the need to find a stable methodological framework in the construction of composite indicators (CIs) in order to address the methodological challenges including those of sensitivity and uncertainties related to methods used. As CIs are well-known to be essential in public debate, their methodological construction must be known by a large public. Illustrating CIs’ construction steps by a simple indicator, the paper aims to “democratize” this disciplinary field which is still a black box for some researchers but also to show how composite scores are sensitive to methods used and then, its impacts on policies. For example, in the Sustainable Development Indicator case, the geometric aggregation system is favorable to emerging countries which lead the ranking table whereas high income countries (which are leaders in the linear and equal weight system) except Australia, are misclassified. Uncertainty and sensitivity analysis confirm these results showing that the indexes’ scores seem to be influenced by the orientation (implied theoretical framework) given by its sponsors including policy makers. Regarding the validity of the index, correlation tests with some lights and well known indicators, reveal very consistent results.

The Composite Indices (CI) are essential for policy-makers. They can be used to guide public policy. The same tools are used to evaluate the performance of public equities. However, they are subject to debate, as there are no standard rules for their construction. This paper discusses the methodological issues in the development of CI. It illustrates them by building a simple sustainable development index for 15 countries. Following the basic steps, the results obtained by the arithmetic mean show that in general, high-income countries, except the USA, have a higher 0.7 index. Emerging countries are the least sustainable of the sample, the developing countries are in an intermediate position. The geometric method provides mixed results. With this method, it is the emerging economies that become leaders in the standings and rich countries, except Australia, saw their index to deteriorate sharply. The sensitivity analysis indicates that the scores and rankings of countries are sensitive to the methods used. It confirms the uniqueness of the BOD method. The uncertainty weighting methodologies ranges from 1.27% to 95.16% in developing countries and emerging countries against 23% on average for the developed countries., Les Indices Composites (IC) sont indispensables pour les décideurs publics. Ils peuvent servir à orienter les politiques publiques. Les mêmes outils sont utilisés pour évaluer les performances des actions publiques. Cependant, ils sont sujets à débats tant il n'existe pas de règles standard pour leur construction. Cet article discute des aspects méthodologiques dans l'élaboration des IC. IL les illustre en construisant un indicateur simple de Développement Durable pour 15 pays. En suivant les étapes essentielles, les résultats obtenus par la moyenne arithmétique montrent que dans l'ensemble, les pays à revenus élevés, exception faite des USA, ont un IDD supérieur 0,7. Les pays émergents sont les moins soutenables de l'échantillon, les PED étant dans une position intermédiaire. La méthode géométrique fournit des résultats plus nuancés. Avec cette méthode, ce sont les pays émergents qui deviennent leaders au classement et les pays riches, excepté l'Australie, ont vu leur indice se détériorer très fortement. L'analyse de sensibilité indique que les scores et les classements des pays sont sensibles aux méthodes utilisées. Elle confirme la particularité de la méthode BOD. L'incertitude associée aux méthodes de pondération varie entre 1,27% à 95,16% pour l'indice des PED et les pays émergents contre 23% en moyenne pour celui des pays développés.