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Table 3 Results of ADF test for unit root 1982–2021 data

From: Effects of crude oil prices on copper and maize prices

 

With constant

With constant and trend

Without constant and trend

t-statistic (p value)

t-statistic (p value)

t-statistic (p value)

LOG_MAIZE

− 1.9124 (0.3265)

− 2.9578 (0.1455)

0.4227 (0.8044)

LOG_COPPER

− 1.1693 (0.689)

− 2.4639 (0.3461)

0.9403 (0.9079)

LOG_CRUDE_OIL

− 1.6902 (0.4356)

− 2.9765 (0.1400)

0.0494 (0.6981)

d(LOG_MAIZE)

− 16.4611*** (0.000)

− 16.4612*** (0.000)

− 16.4635*** (0.000)

d(LOG_COPPER)

− 6.0474*** (0.000)

− 6.0452*** (0.000)

− 5.9588*** (0.000)

d(LOG_CRUDE_OIL)

− 14.2595*** (0.000)

− 14.2537*** (0.000)

− 14.2684*** (0.000)

Result

I(1)

I(1)

1(1)

  1. (***) Significant at the 1% and t value without ***not significant, b: lag length based on AIC, probability based on MacKinnon [25] one-sided p values. I(1) Integrated of order 1