Panel Data calculations

I am a total beginner to Panel Data and I’ve always been bad with Maths, Economics, Statistics etc. I hope I can find some help here.

I need to build a Panel Data. I have Data (1) with Country, Year (in total 18 yrs), Control Variables and the Dependent and Independent Variable. I needed additional Control Variables and used other Databanks to get the Data (2) such as GDP, Population, Education. The Control Variables in Data (1) are in % e.g., 0.28. The Control Variables in Data (2) are like this: GDP e.g., 1260.61, Population e.g., 22645130, and Education e.g. 42.61.

I think bc my Control Variables in Data (1) are in % I need to also do that for my Control Variables in Data (2), right? And I guess Education is already shown as %. Meaning I need the percentage of GDP and Population. I only know that Data (1) is a National-level Dataset, does that mean I create the mean of GDP by dividing each GDP per year with the total years?

Or Is that something that does not need to be done to GDP and Population since these are variables on Country level?

Hi @alkam and welcome!

We try to keep this forum focused on questions that relate directly to Stan. For general statistical design questions like this one, you might have more luck at