Issues in measuring real structural change in energy economic studies: annual growth rates not sectoral shares

To understand the relation between energy use and economic growth, it is important to correctly manipulate economic data at sectoral level to allow a proper interpretation of the effects of structural change on the dynamics of energy intensity. Here, we discuss the selection of suitable economic time series and how to properly treat and manipulate them in energy intensity analysis, taking the Portuguese economy as a case study. First, our results, comparing current and constant prices series (1960-2024), highlight the importance of using constant price series. Second, our findings empirically show how annual growth rates are preferable to sectoral shares. Third, through three practical examples of Index Decomposition Analysis (IDA) (1960-2014), we empirically show how decomposition results may be both quantitatively and qualitatively biased for analyses spanning long periods if the chosen decomposition method is not consistent with the way constant prices series have been derived.