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| Variable symbol | Variable name | Variable definitions |
| Dependent variable | RD | R & D investment | The natural logarithm of the R & D investment in this period |
| Independent variables | ETR | Corporate tax burden | (income tax expense ? deferred income tax expense)/total profit |
| Control variables | LASTRD | Last R & D investment | RD lag phase I |
| LASTETR | Last corporate tax burden | ETR lag phase I | |
| ROE | Profitability | The total profit/total assets | |
| SIZE | Company size | The natural logarithm of total assets | |
| LEV | Asset-liability ratio | Total debt/total assets | |
| SALE | Total profit | Natural logarithm of total profit |