Abstract
The article refers to the new Synthetic Efficiency Indicator for Economic Growth (SEI-EG) proposed in an earlier publication. Research from 2016–2018 in 11 EU countries revealed small nations were notably more effective at sustainable growth than their larger counterparts. This prompted the authors to ask about the differences between small countries with developed economies and small countries with lower levels of development joining the EU in 2004. The article aims to determine the relative efficiency of transforming growth inputs and debt into sustainability outcomes for small countries in the EU using the SEI-EG index over the period 2016–2020. The study group symmetrically includes six countries each from developed economies and six countries that joined the EU in 2004. The adopted indicator complements the expanded SDGs and aligns with the trend linking research inputs to sustainable development effects.