Table 1

Results of ADF and PP unit root tests of the variables in level and first difference

GDPREERGMPoil
ADFPPADFPPADFPPADFPPADFPP
Unit root tests of variables in levels
Constant−1.29 (0.62)−1.41 (0.57)−3.63*** (0.007)−2.82* (0.06)−2.23 (0.19)−2.68* (0.08)−1.37 (0.58)−1.58 (0.48)−1.80 (0.37)−1.86 (0.34)
Constant and Trend−1.59 (0.78)−1.23 (0.89)−4.29*** (0.006)−3.11 (0.11)−2.67 (0.25)−2.45 (0.34)−1.30 (0.87)−1.12 (0.91)−1.93 (0.62)−1.93 (0.62)
Unit root tests of variables in first difference
Constant−4.58*** (0.00)−4.59*** (0.00)−5.88*** (0.00)−5.66*** (0.00)−5.95*** (0.00)−5.98*** (0.00)−4.99*** (0.00)−4.97*** (0.00)−6.65*** (0.00)−6.60*** (0.00)
Constant and Trend−4.73*** (0.00)−4.74*** (0.00)−55.83*** (0.00)−5.79*** (0.00)−6.26*** (0.00)−6.26*** (0.00)−5.11*** (0.00)−5.04*** (0.00)−6.68*** (0.00)−6.63*** (0.00)

Note(s):*, **, *** imply rejection of the null hypothesis at the 10%, 5% and 1% significance level, respectively. Lag length is based on SIC. P-values are in parenthesis. The null hypothesis is that the series is non-stationary

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