i am working on oil price shocks where i have divided price shocks into positive and negative shocks .i have taken sample of oil importing economies divided into 3 groups on the basis of oil imports A(0-10%oil imports)=22 B(10-20%)= 45 C(20-30%)=12 .the dependent variable is industrial production(lip) independent variables in the analysis are exchange rate(lex) (both used in log form), oil price shocks negative (opn),oil price shocks positive (opp)
i am using panel ARDL technique using syntax(stata 14)
xtpmg d.lip d.opn d.opp d.lex, ec(ec) lr(l.lip opn opp lex ) mg replace
expression (-_b[opn]/_b[L.lip]) evaluates to missing
r(498);
the above error appears for group A and B and not for C group.
suggestion required .