econometric data I have a quit straight forward question: I have a variable which is coal rents measured in 2009 US Dollar. I would like to set this variable in relation (ratio) to another variable which is PPP Converted GDP Per Capita (Chain Series), at 2005 constant prices. $\frac{\rm coal \;rent}{\rm GDP(ppp)}$ I would like to run some regressions with this variable as my independent variable. However I´m not sure whether I have to account for inflation from 2005-2009 when doing the ratio of $\frac{\rm coal \;rent}{\rm GDP(ppp)}$.....I dont have much economics backround :) maybe some of you are able to give me a theoretical as well as a practical hint.... thx and happy new start :)

Mathematically, you can do whichever you like. They are both well defined computations. Since your GDP data is adjusted for inflation, it seems more logical to have your coal rents in constant dollars. To do so, divide the coal rents in each year by the ratio of that year's inflation measure to the measure in the base year (presumably 2005).