Please I am writing my thesis for my masters program. I am estimating the gravity model and I need guidance on the command to use. firstly I have dummy variables, some bilateral, while some are country specific. I guess this means I am using a random effects approach right?. Also when trying to estimate the regression equation, I want to use the Pseudo Poisson Maximum Likelihood (ppml).so i installed ppml on stata and ran the command like this 'ppml dependent variable independent variable. unfortunately the main variable came out with a sign that was not expected. Then I used xtpoisson dependent variable independent variable and i got another result. Please which command is right? and is there something else I am supposed to do that I am not doing?
↧