| 1 | A | B | C | D | E |
| --- | --- | --- | --- | --- | --- |
| 2 | first-stage effects of compulsory schooling on high school completion |  |  |  |  |
| 3 | type of compulsory schooling controls in the estimator | entry and dropout age fixed effects | entry versus dropout age effects | effect of total mandatory years | effect of total mandatory years |
| 4 |  | coefficient estimates |  |  |  |
| 5 | fixed effects |  |  |  |  |
| 6 | entry age = 7 | 0.010 | .. | .. | .. |
| 7 | entry age = 8 | -0.029 | .. | .. | .. |
| 8 | dropout age = 15 | 0.003 | .. | .. | .. |
| 9 | dropout age = 16 | 0.013 | .. | .. | .. |
| 10 | dropout age = 18 | 0.028 | .. | .. | .. |
| 11 | linear effects |  |  |  |  |
| 12 | entry age | .. | -0.013 | .. | .. |
| 13 | dropout age | .. | 0.008 | .. | .. |
| 14 | combined effect |  |  |  |  |
| 15 | mandatory years | .. | .. | 0.010 | 0.010 |
| 16 | additional controls |  |  |  |  |
| 17 | age fixed effects | yes | yes | yes | yes |
| 18 | cohort fixed effects | yes | yes | yes | yes |
| 19 | birth-province fixed effects | yes | yes | yes | yes |
| 20 | birth province-cohort trends | yes | yes | yes | yes |
| 21 | institutional covariates | yes | yes | yes | yes |
| 22 | individual covariates | no | no | no | yes |
| 23 | labour income controls | no | no | no | yes |
| 24 | labour income 10-piece spline | no | no | no | yes |
| 25 |  | estimates |  |  |  |
| 26 | statistics |  |  |  |  |
| 27 | r-squared | 0.042 | 0.041 | 0.041 | 0.118 |
| 28 | f-test of excluded instruments | 11.080 | 15.180 | 26.730 | 26.540 |
| 29 |  | number |  |  |  |
| 30 | observations | 477,813 | 477,813 | 477,813 | 473,608 |

Question: how many different approaches to account for compulsory schooling laws are used?
Answer: 3