Thus, all countries and economies contribute equally to ESCS scores. However, for the purpose of reporting, the values of the ESCS scale are standardised to have a mean of zero and a standard deviation of one for the population of students in OECD countries, with each country given equal weight. In order to allow for trend analyses, in PISA 2015, the ESCS was computed for the current cycle and also recomputed for the earlier cycles using a similar methodology (see PISA 2015 Technical Report (OECD, forthcoming!).