<sup>3</sup> Replacement of urban innovation index

To avoid regression estimation bias due to the indicator measure, the core explained variable in the benchmark regression in the previous section, the urban innovation index (Innovation), was replaced. Patents are an effective indicator of innovation levels and can reflect the level of innovation output of a city. Thus, this study conducted robustness testing by replacing the urban innovation index with the number of patents granted (Patent) as obtained from www.zhuanli.com (accessed on 24 March 2020) for each city as the explained variable (Table 7), and proved the consistency with the baseline regression result, demonstrating the robust regression results in this study.

**Table 7.** Results of robustness tests after replacing the urban innovation index.


Note: \*\*\* and \*\* represent the significance at the 1% and 5% levels, respectively. The *t*-values are in parentheses.

According to the green patent list and the international classification code provided by the World Intellectual Property Organization (WIPO), we summed up green patent data at the city level and divided them into two parts: green patent application and green patent authorisation. According to the regression results in Table 8, the impact of environmental regulation on green patents is significantly negative at the level of 1% for both green patent applications and green patent grants. This means that environmental regulation policies will lead to the decline of green innovation patents. This is consistent with the original regression results, indicating that the original conclusion has good robustness.

**Table 8.** Results of robustness tests after dividing green patent into two parts: green patent application and green patent authorisation.


Note: \*\*\* and \*\* represent the significance at the 1% and 5% levels, respectively. The *t*-values are in parentheses.
