hi all, i need help , iam using a synthetic control group , for a policy inversion for five cases(countries) with a control group of 15 countries to each case , i set the data and declare it as a bnlanced panel , when i tried to follow stata command i come up with the error (control units: for at least one unit predictor opr_n is missing for ALL periods specified) , my variables are
any help please
id | country | year | oex_n | opr_n | gdp | gdpp | gev | eu | fdi_n |