Robustness tests: alternative measures of firm innovation
| Panel A: alternative horizon for patents filed and cited | ||||
|---|---|---|---|---|
| Dep. Variable | (1) | (2) | (3) | (4) |
| Log(1+patents) | Log(1+citations adj.) | Log(1+patents) | Log(1+citations adj.) | |
| t+1 | t+1 | t+3 | t+3 | |
| TFE | 0.071*** | 0.066*** | 0.079*** | 0.066*** |
| (2.94) | (2.75) | (3.31) | (2.77) | |
| Observations | 10,336 | 10,336 | 10,336 | 10,336 |
| Adjusted R2 | 0.908 | 0.891 | 0.897 | 0.872 |
| Control variables | Yes | Yes | Yes | Yes |
| Year FE | Yes | Yes | Yes | Yes |
| Firm FE | Yes | Yes | Yes | Yes |
| Panel A: alternative horizon for patents filed and cited | ||||
|---|---|---|---|---|
| Dep. Variable | (1) | (2) | (3) | (4) |
| Log(1+patents) | Log(1+citations adj.) | Log(1+patents) | Log(1+citations adj.) | |
| TFE | ||||
| Observations | 10,336 | 10,336 | 10,336 | 10,336 |
| Adjusted | 0.908 | 0.891 | 0.897 | 0.872 |
| Control variables | Yes | Yes | Yes | Yes |
| Year FE | Yes | Yes | Yes | Yes |
| Firm FE | Yes | Yes | Yes | Yes |
| Panel B: number of patents and citations without taking the logarithm or excluding zero patents | ||||||
|---|---|---|---|---|---|---|
| Dep. Variable | (1) | (2) | (3) | (4) | (5) | (6) |
| Numb. of patents t+2 | Numb. of patents, excluding zero-patent firms t+2 | Numb. of adjusted citations t+2 | Numb. of adjusted citations, excluding zero-patent firms t+2 | Numb. of patents, excluding zero-patent firms t+2 | Numb. of adjusted citations, excluding zero-patent firms t+2 | |
| TFE | 15.123*** | 30.961*** | 14.286** | 27.647** | 0.082*** | 0.077* |
| (3.09) | (2.99) | (2.29) | (1.99) | (2.63) | (1.84) | |
| Observations | 10,336 | 4,727 | 10,336 | 4,723 | 4,727 | 4,723 |
| Adjusted R2 | 0.833 | 0.826 | 0.791 | 0.781 | ||
| Estimation method | OLS | OLS | OLS | OLS | NB | NB |
| Control variables | Yes | Yes | Yes | Yes | Yes | Yes |
| Year FE | Yes | Yes | Yes | Yes | Yes | Yes |
| Firm FE | Yes | Yes | Yes | Yes | Yes | Yes |
| Panel B: number of patents and citations without taking the logarithm or excluding zero patents | ||||||
|---|---|---|---|---|---|---|
| Dep. Variable | (1) | (2) | (3) | (4) | (5) | (6) |
| Numb. of patents | Numb. of patents, excluding zero-patent firms | Numb. of adjusted citations | Numb. of adjusted citations, excluding zero-patent firms | Numb. of patents, excluding zero-patent firms | Numb. of adjusted citations, excluding zero-patent firms | |
| TFE | ||||||
| Observations | 10,336 | 4,727 | 10,336 | 4,723 | 4,727 | 4,723 |
| Adjusted | 0.833 | 0.826 | 0.791 | 0.781 | ||
| Estimation method | OLS | OLS | OLS | OLS | NB | NB |
| Control variables | Yes | Yes | Yes | Yes | Yes | Yes |
| Year FE | Yes | Yes | Yes | Yes | Yes | Yes |
| Firm FE | Yes | Yes | Yes | Yes | Yes | Yes |
Note(s): Panel A reports the OLS regressions using patent variables over alternative horizons than ones examined in Table 3: t+1 and t+3. Panel B presents the robustness tests for Table 3 for the number of patents and adjusted citations at t+2, but without taking the logarithm and/or excluding zero-patent firms. Specifications (1)–(4) in Panel B show the results from the OLS regressions, while specifications (5) and (6) in Panel B present the results of the negative binomial regressions. Control variables (not shown) include the logarithm of CEO age, the logarithm of CEO tenure, firm size, the logarithm of firm age, capital expenditures, R&D expenditures and the logarithm of the number of employees. Standard errors are clustered at the CEO level. The t-statistics are in parentheses. *, ** and *** indicate statistical significance at the 10%, 5% and 1% levels, respectively. Standard errors are clustered at the CEO level. The t-statistics are in parentheses.*, ** and *** indicate statistical significance at the 10%, 5% and 1% levels, respectively