| Year effect | Yes | Yes | Yes | Yes | Yes | Yes |
| Code effect | Yes | Yes | Yes | Yes | Yes | Yes |
| N | 7384 | 5784 | 7384 | 5784 | 7384 | 5784 |
| R-sq | 0.5364 | 0.5755 | 0.5569 | 0.6014 | 0.5578 | 0.6030 |