Currency-trading strategies are losing the most in two decades as the volatility that’s boosted volume and profits for investment banks erodes the ability of investors to make money. Three out of four Royal Bank of Scotland Group Plc indexes of foreign-exchange trading strategies are down this year, including a 2.7 percent drop through September for its carry trade index. Deutsche Bank AG’s dollar-denominated Currency Returns Index has fallen 3.4 percent, the biggest drop since a 4 percent slide in 1991. The Stark Currency Traders Index and a Barclays Plc index have declined by 8.6 percent and 0.4 percent. Whipsawed ... (full story)