First of all run a simple VAR, set the maximum lag(which is the discretion of the researcher) and choose the optimal lag based on either AIC, BIC(SIC), FPE or HQC. For goodness of fit, use the AIC or FPE  if observations are less than 60 and the HQC if observations are more than 60( Khim Liew,2004):http://www.accessecon.com/pubs/eb/2004/volume3/EB-04C20021A.pdf ________________________________ From: Surya Dev <sungodno1(a)yahoo.com&gt; To: Gretl-users(a)lists.wfu.edu Sent: Saturday, November 19, 2011 8:03 AM Subject: [Gretl-users] unit root test how do you choose optimal lag while carrying out ADF test in Gretl? _______________________________________________ Gretl-users mailing list Gretl-users(a)lists.wfu.edu http://lists.wfu.edu/mailman/listinfo/gretl-users