Investors have not known which way to look all summer, as asset prices have jerked from highs to lows day to day amid geopolitical threats, interest rate worries and scant volumes and volatility.

Global markets have been rocked by tensions between Russia and the West, sparked by Russia's annexation of Crimea in March this year. At the same time, market watchers have been focusing on whether the European Central Bank will announce new monetary stimulus and the timing of interest rate rises in the U.K. and the U.S.