The definition of the phenomenon should provide a clear and concise idea of what the composite index is intended to measure. The phenomenon should be defined positively (not by negating other things), in unambiguous terms and in a way that is consistent with previous research. The definition should not be too technical, allow for multiple interpretations, be circular, tautological or self-referential. In particular, the researcher should specify the nature of the phenomenon, including (i) the type of property the phenomenon represents (e.g. a perception, an outcome, a performance), and (ii) the entity (unit) to which it refers (e.g. a person, an organization, a country) (MacKenzie et al. 2011).