Sustainability assessment by fuzzy evaluation (SAFE) is a model for the numerical assessment of sustainability.
SAFE, uses fuzzy logic reasoning and basic indicators of environmental integrity, economic efficiency and social welfare, and derives measures of human, ecological, and overall sustainability.
The model is amended by an imputation procedure to fill in missing data, rule bases are compiled algebraically, and sustainability thresholds are defined so as to reflect expert opinion and international agreements and norms.
SAFE is a hierarchical fuzzy inference system. It uses knowledge encoded into “if-then” rules and fuzzy logic to combine 75 inputs, called basic indicators, into more composite variables describing various environmental and societal aspects and, finally, provides an overall sustainability index in [0, 1].