A sustainable society index (SSI) developed by the Sustainable Society Foundation (SSF) has been designed to measure the sustainability of 151 countries over the world in terms of human, environmental and economic well-being dimensions. The purpose of SSF's SSI is to share global, integrated and scientifically based information and serve as a tool to measure the level of sustainability of a country in absolute terms and in comparison with other countries. The SSF provided the framework and the data for this study. The aims of this study were to test different alternatives that would enable to take interactions of the sustainability indicators into account and accomplish a more non-compensatory composite index, which presents more of a stronger sustainability view instead of weak sustainability. The tested methods included additive aggregation rule with interaction terms for the indicators, multiplicative aggregation rule, weighting of the decision hierarchy and constructing piecewise linear models with threshold values to calculate the indicator scores for each country from the raw data. The acquired results were compared to the redesigned SSI-2012 developed by the SSF. According to the results of this study, the new framework and geometric mean used as aggregation method in the redesigned SSF's SSI-2012 did not fully succeed in its aims towards more non-compensatory composite index. The results of the tested methods showed that the most useful manner to construct composite indices such as SSI would be the use of multiplicative aggregation rule applying weighting based on expert elicitation, and constructing new calculation rules with thresholds for the indicator scores, thus considering the strong sustainable view already at the level of indicator scores. However, all these issues need further studying and development including new comprehensive weighting task, expert judgment task for determining the threshold values and constructing the piecewise models for calculation of the indicator scores.
