| variable | ADF test | pp test | results | ||
| Level value | First order difference | Level value | First order difference | ||
| lny | −2.263 | −4.024** | −2.36 | −4.47* | I (1) |
| lnx | −2.65 | −2.23*** | −2.08 | −2.25** | I (1) |
| lnx2 | −2.09 | −2.19** | −3.21 | −2.22* | I (1) |