Normalization in sustainability assessment: Methods and implications

Abstract

One approach to assessing progress towards sustainability makes use of diverse indicators spanning the environmental, social, and economic dimensions of the system being studied. Given the use of multiple indicators and the inherent complexity entailed in interpreting several metrics, aggregation of sustainability indicators is a common step after indicator measures are quantified. Diverse indicators have different units of measurement, and normalization is the procedure employed to transform differing indicator measures onto similar scales or to unit-free measures. It is often difficult for stakeholders to make clear connections between specific indicator measurements and resulting aggregate scores of sustainability. Normalization can also create implicit weightings of indicator measures that are independent of actual stakeholder preference or explicit weighting. This paper explores normalization methods utilized in sustainability assessment including ratio normalization, target normalization, Z-score normalization, and unit equivalence normalization. A mathematical analysis of the impact of changes in raw indicator data measurements on an aggregate sustainability score is developed. Theoretical results are clarified through a case study of data used in assessment of progress towards bioenergy sustainability. Advantages and drawbacks associated with different normalization schemes are discussed within the context of sustainability assessment.