A formative approach to index construction

We adopted a formative approach in developing the EfDI and its subindexes, focusing on theoretical considerations rather than internal consistency (see Coltman et al. 2008). This approach enables us to create a measure that captures the relationship between education and democratic competences comprehensively. Consequently, the measure is multidimensional, meaning that the same overall score across different countries can reflect varying values on the seven educational areas as its constituting components. While this approach may weaken measurement equivalence, leading to challenges in comparing like with like (Aléman & Woods, 2016), external validity—a measure’s ability to predict or be predicted by other phenomena— in our view is an equally important criterion to judge the quality of a composite index with (see also Datler et al., 2013). Welzel and Inglehart (2016) support the idea that a composite index with lower internal consistency but higher external validity is not only acceptable but preferable. A reflective approach, which concentrates on internal consistency and measurement equivalence, would have limited our ability to construct a comprehensive EfDI measure, a limitation we believe would be more significant than any decrease in internal consistency. However, as a concession to this approach and in line with Welzel and Inglehart’s guidance, we made sure that the indicators for the educational areas included in the EfDI are not negatively correlated. It would not make sense to include negatively correlated indicators in an index as they would cancel each other out.