It covers final energy demand, energy conversion and transport, and primary energy supply (hence, in principle the entire energy system). The difference in the SSDI and the S/D index is that the SSDI was adapted to be able to work with the only available consistent data available for the past 40 years, i.e. the IEA Energy Statistics. The applicability of the scoring rules (see below) has also been simplified and adapted from the European Union and Norway to the whole of the OECD.