The State Street Investor Confidence Index posted a big jump in January as North American investors felt optimistic about the strategy being pursued by the Federal Reserve Bank, the people compiling the index said Tuesday.

The index, which has a neutral reading of 100, seeks to measure investor confidence by analyzing the actual buying and selling patterns of institutional investors, said State Street Global Exchange, a unit of State Street Corp. State Street Corp. is a Boston-based financial-services company.

January’s global reading for the index was 114.4, up 18.6 points from December’s revised reading of 95.8. The reading was the largest month-to-month jump in more than four years, State Street Global Exchange said.

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In a statement, Jessica Donohue, a senior managing director at State Street Global Exchange, commented on the index’s latest reading.

“Policy uncertainty was reduced in the US and confidence was boosted by optimism over the Fed’s policy of forward guidance, which may help anchor low interest rates going forward,” Donohue said. “It will be critical to see how sentiment holds up during the debt ceiling debate given the renewed concerns over emerging market growth.”