Comparing GDP contractions between Russia and US 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.
In Rogoff's article (at least current version) the first sentence you quote links to IMF's World Economic Outlook Database. 

My guess is that when he is referring to output he means Gross domestic product, constant prices. Looking up the numbers in the database we have 63038.4 billions of 2011 rubles in 2014 and 61097.5 in 2016 which translates to 3.1% decline (negative growth). 

If I use per capita numbers than that also gives 3.1% decline which I guess is "comparable" to 4% decline.