Augmented Dickey–Fuller (ADF) test is used in this study. It is a
version for larger and more complicated set of time series models. It was assumed that
the error term ݁௧ are correlated. It is negative number, the more negative is the
stronger the rejection of the null hypothesis (ܪ ߩ ൌ 1) that it is unit root at a
level of confidence. Then those three DF tests are: