I was reading Rogoff's piece on the Russia's economic outlook, and in a paragraph, he states
The shock to the real economy has been severe, with Russia suffering a decline in output in 2015 and 2016 comparable to what the United States experienced during its 2008-2009 financial crisis, with the contraction in GDP totaling about 4%.
I'm wondering how did they reach this figure. I was trying to redo the calculations, this time with OECD data on GDP, but none of the figures obtained are comparable - I just did $GDP_{t+1}/GDP_{t}=1+gr$ For Russia, I got 6-7%, and USA 2-3%, depending whether we use GDP or GDP per capita.
Any help would be appreciated.