3.2.4. Control Variables

Based on previous studies, such as Tong Yun [60], the current studies mostly analyze the effects of the economic level, environmental regulation, technological innovation and foreign investment on urban green economic efficiency and carbon emission intensity, while variables such as industrial structure, government intervention and financial development are gradually added as the research progresses. To reduce the estimation bias, the following control variables are chosen in this paper: industrial structure (is), using the share of secondary industry value added in GDP as a proxy variable [21,61]; economic development (eco), using the GDP per capita representation [59]; foreign investment (fdi), using the share of foreign direct investment in urban GDP as a proxy variable [14]; technological innovation (ino), using the share of science and technology expenditure in urban GDP [14]; environmental regulation (env), characterized by the comprehensive utilization rate of the industrial fixed waste [25].
