| ig | Coef. | Std. Err. | z | P > |z| |
| wig | 0.027 | 0.005 | 6.01 | 0.000 |
| oig | −0.071 | 0.051 | −1.39 | 0.164 |
| pig | −0.006 | 0.001 | −4.72 | 0.000 |
| tig | 0.007 | 0.002 | 3.08 | 0.002 |