| Variable | regression coefficient | S.D. | T | P |
| lnZ1 | 0.0865 | 0.0350 | 2.47 | 0.014** |
| lnZ2 | −0.2668 | 0.0687 | −3.88 | 0.000*** |
| lnZ3 | 0.0501 | 0.0439 | 1.14 | 0.255 |
| lnZ4 | 0.2588 | 0.0168 | 1.54 | 0.126 |
| lnZ5 | −0.0469 | 0.1762 | −2.66 | 0.008*** |