The global reading climbed seven points in May to 120.8, a welcome contrast to the 2.3 point dip recorded last month. Optimism was particularly notable among North American investors, who pushed the region's index up eight points to 129.4.

“A lower dollar, stabilizing energy prices, and reduced expectations of an imminent rate hike provided tail winds to North America sentiment,” said State Street Associates' Kenneth Froot.

“Investors must now wait and see whether a rebound in second quarter growth will lead to more hawkish statements from the Federal Reserve.”

Asia also saw positive movements, rising 7.4 points to 98.6 over the month, which State Street attributed to favourable policy maneuvers in China. Meanwhile in Europe, sentiment suffered with a 5.5 point dip to 103.8. Here, investors were unnerved by a rising euro, increased sovereign yields, and a continued Greek debt funding crisis.

The State Street Investor Confidence Index looks at investors' allocation to equities to determine changes in confidence or risk appetite.