after preceding discussion it is obvious that this can again be only a partial input to the ongoing discussion about what energy supply security means for different countries and different stakeholders this index is normalised to range from extremely low security to extremely high security it covers final energy demand energy conversion and transport and primary energy supply and hence in principle the entire energy system the sd index is also at the basis of the ssdi employed in chapter of this publication to track the evolution of the energy supply situation in selected oecd countries over the past years in a systematic manner the difference in the ssdi and the sd index is essentially that the ssdi was adapted to be able to work with the only available consistent data available for the past years ie the iea energy statistics