R Unit Root Tests
From adf.test help
package: tseries
x <- rnorm(1000) # no unit-root
adf.test(x)
Augmented Dickey-Fuller Test
data: x
Dickey-Fuller = -10.0235, Lag order = 9, p-value = 0.01 <- Safe to reject null hypothesis that x has a unit root
alternative hypothesis: stationary
Warning message:
In adf.test(x) : p-value smaller than printed p-value
PP.test(x)
Phillips-Perron Unit Root Test
data: x
Dickey-Fuller = -33.4783, Truncation lag parameter = 7, p-value = 0.01<- Safe to reject null hypothesis that x has a unit root
y <- diffinv(x) # contains a unit-root
adf.test(y)
Augmented Dickey-Fuller Test
data: y
Dickey-Fuller = -1.7578, Lag order = 9, p-value = 0.6808 <- Fail to reject null hypothesis that x has a unit root
alternative hypothesis: stationary
PP.test(y)
Phillips-Perron Unit Root Test
data: y
Dickey-Fuller = -1.9082, Truncation lag parameter = 7, p-value = 0.6172 <- Failto reject null hypothesis that x has a unit root
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