Investor confidence in North America continued to weaken in September, according to State Street's Investor Confidence Index.

The index fell by 3.2 points in September to 81.1 from a month earlier.

The sentiment in North America echoes global cues, with the Global Investor Confidence Index also declining to 86.9 from August's 91.0. The Asian Investor Confidence Index followed by falling 5.6 points to 87.6 points. European investors surprisingly reported an increase in confidence and risk appetite, with the European index climbing 4.0 points to 105.0 from 101.0 in August.

The index was formulated by Harvard University professor Kenneth Froot and Paul O'Connell of State Street Associates. The index measures actual trade patterns of institutional investors and does not reflect investor opinion. An index of 100 is considered to be a neutral sentiment with anything above and below that benchmark showing increased and decreased risk appetite respectively.

The low investor confidence numbers for North America come in as a surprise given the recent measures taken by the Federal Reserve to boost the economy.

"The third consecutive decline in confidence among North American investors is more puzzling, especially given recent announcements by monetary policy makers on both sides of the Atlantic," Froot said.

However, the researchers have noted a significant improvement in trades in recent weeks.

"One point worth noting is that we observed a pronounced improvement in tone from the first week of September onwards," O'Connell said.