I'm conducting a research in which the real exchange rate serves as a variable. A quick literature review shows that we can use the product of the nominal exchange rate and the ratio between the US GDP deflator and my country GDP deflator as a proxy for the real exchange rate. However, these two deflators has different base years: 2000 for the first one and 2006 for the second one. What should I do? Do I need to transform their data to a same base year or it doesn't matter?