Bro seems like your equation is incomplete. GDP = Consumption + Investment + Government Expenses + Net Export ( Net Export - Net Import) but you just have GDP = C + I , I am quite not sure about that. If anyone taking Econometrics and needs good Econometrics research paper for your final, holla at me. I did a research on Determinants of Traffic Mortality Rate in U.S in Cross Section data for 2004 for my final. I will hand it to you.