The ARDL bounds testing approach of cointegration is developed
by Pesaran and Shin (1999) and Pesaran et al. (2001). The ARDL
cointegration approach has numerous advantages in comparison
with other cointegration methods such as Engle and Granger
(1987), Johansen (1988), and Johansen and Juselius (1990) procedures:
(i) no need for all the variables in the system be of equal
order of integration, (ii) it is efficient estimator even if samples are
small and some of the regressors are endogenous, (iii) it allows
that the variables may have different optimal lags, and (iv) it employs
a single reduced form equation.