*3.2. Energy Diversity Indices*

As one of the types of indices interrelated with energy dependence, the energy supply diversity indices have been quantified by several analytical approaches [34]. Stirling presented research focusing on diversity in the energy sector and suggested three important elements: variety, balance, and disparity [35,36]. As the disparity of energy options is not easily quantified, indices without consideration of disparity are widely applied in the measurement of diversity [6,10,34]. Hill identified an entire family of possible quantitative assessments of diversity in terms of proportional abundances of the species in a sample [37]. As the Hill index family, the *SWI* and *HHI* are the most commonly used indices in the energy sector. These two indices are applied in this study to evaluate energy diversity, especially the balance and variety of energy options in Korea.
