| Variable type | Variable name | variable symbol | variable declaration |
| Explained variable | R&D innovation | RD | Annual R&D expenses/operating income |
| Explanatory variable | Economic policy uncertainty | EPU | As shown in model (2) |
| Control variable (CV) | Company size | SIZE | Find the natural logarithm of total assets at the end of the year. |
| investment opportunity | GR | Annual growth rate of operating income | |
| Operating cash flow ratio | CFO | Net cash flow from operating activities/total assets at the end of the year | |
| Asset-liability ratio | LEV | Total liabilities/assets at the end of the year | |
| Debt term | STD | Current liabilities/total liabilities at the end of the year | |
| The shareholding ratio of the largest shareholder | FH | Number of shares held by the largest shareholder/total number of shares | |
| asset structure | FS | Amount of non-current assets/total assets at the end of the year | |
|
| Property right nature | STA | The actual controller is state-owned, and the value is 1; otherwise, it is 0. |
|
| Year | Year | dummy variable |
|
| industry | Indus | dummy variable |