Hello, I would like to regress the independent variable GINI (Gini Index) on the dependent variable GDPpc (GDP per capita growth). For GDPpc to reach its stationary form, its first difference had to be taken. However, GINI was already in a stationary form.
I tried two different regressions. One with GDPpc and GINI being both in their first difference and one with only GDPpc being in its first-difference.
The first regression (d1_GDPpc, d1_GINI) yields a really high p-value, while the second regression (d1_GDPpc, GINI) yields a low enough p-value for the effects to be statistically significant.
My questions are the following:
Is it possible to regress variables in their first difference with variables in their level? Which regression model should I choose?