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Test for Unit root by applying ADF.
| Unit root (level) | Intercept | Intercept and Trend | Decision |
|---|---|---|---|
| OPVt | −3.726*** | −4.342*** | I(0) |
| GDPt | −1.559 | −4.570*** | I(0) |
| NRt | −3.021 | −3.291 | I(1) |
| REt | −1.233 | −1.381 | I(1) |
| CO2t | −3.450* | 3.095* | I(0) |
| Unit root (first difference) | |||
| OPVt | −3.541* | −3.400* | I(0) |
| GDPt | −6.777 | −4.821 | I(0) |
| NRt | - 3.811*** | - 3.701 | I(1) |
| REt | −6.903 | −3.288 | I(1) |
| CO2 | 11.850* | −11.317* | I(0) |
