Types of Indicators: Descriptive, Performance and Composites
A distinction can be made between descriptive, performance and composite indicators. Descriptive indicators 'can be dichotomous, number, grade, time series, or ratios or other derived functions', and indicate the state of a system (for example, the environment), while leaving specific policy interpretations aside (Gudmundsson 2003, p. 3). The absence of explicit interpretations obviously does not imply neutrality or objectivity. Performance indicators compare indicator values against a standard, target value or benchmark, measuring how well 'someone' is performing, thereby implying that this 'someone' has agency, that is, capacity to influence the course of events. Performance indicators can concern policy inputs, processes, outputs, outcomes, effectiveness or efficiency (Carter et al. 1993). By their very nature, performance indicators therefore already entail a specific type of intended use. Hood (2007, pp. 100-101) further distinguishes target systems, designed to measure performance against an aspirational standard and to help raise levels of performance; ranking systems that compare performance of a given unit with that of another, similar unit; and intelligence systems that do not rank or compare to a standard, but aim merely to build a knowledge base.
Finally, the production of composite indicators1 that aggregate a series of individual indicators into one or a few numbers, on the basis of an underlying model of the multidimensional concept that is being measured (for example, Grupp and Schubert 2010), especially when single indicators cannot capture the richness of a multidimensional concept, has greatly expanded in the past years. While GDP remains the hegemonic composite indicator, recent efforts have concentrated on developing alternative indicators of sustainability, progress and wellbeing as well as an increasing variety of league tables and rankings of countries, public services, and so on (for example, Pinter et al. 2005). The constitution of composite indicators presents methodological challenges relating to choice, weighting and aggregation. A 'milder' variant of composite indicators are 'headline indicators' - a selection of key indicators in a given policy domain, designed to communicate in a concise manner to high-level policymakers and the general public the essence of progress towards main policy objectives.