The Russian ruble is proving surprisingly impervious to the price of oil. The currency of the world’s largest energy exporter has more or less ignored the value of the commodity in the past few months, according to Citigroup Inc. analysts led by Luis Costa. Usually when oil prices fall, so does the currency, but not so recently: Fair value for the currency is 68 rubles to the dollar, according to the analysts’ calculations — based on regression modelling of Brent crude futures and the dollar-ruble exchange rate. The current level is more like 65.8. The ruble has returned the most of any major world currency in 2016 after Brazil’s real and Japan’s yen, attracting investors searching for higher yields amid record central bank stimulus in developed nations. It’s also the best currency for carry trades — which involve borrowing in low-interest rate currencies to buy higher-yielding ones — according […]