Hello,

I am trying to build up panel data for my gravity model. the dependent variable is trade flow of 23 countries to each other from 1980 to 2015. I created ids and managed to identify time variable since there are repeating time values eg: the exports from Albania to Greece in 1980, the exports from Albania to Turkey in 1980..etc. however now I need to add country specific data such as GDP (as independent variable) which occurs 1980 just once whereas 1980 has 22 relationship spesific observation point for each country. How do I match/merge data?