State Street Global Markets reports that its investor confidence index slipped 5.5 points to 83.9 in May.

“During May the confidence of institutional investors in equity markets fell substantially,” said Paul O’Connell of State Street Associates, who co-developed the index with arvard University professor Ken Froot “This was particularly the case for U.S. investors, who have been reducing their exposures to risky assets across their portfolios. The risk appetite of Asian institutional investors, by contrast, improved somewhat.”

“These negative effects were strongest in the first two weeks of May,” added Froot. “This is not too surprising, given the developments in the global debt markets. We are seeing investors moving strongly toward ‘safer’ assets, such as U.S. Treasuries, and away from corporate debt, where spreads have widened. Ratings changes, even after changes in fundamentals, appear to have important impacts on markets and prices.”

The index measures investor confidence on a quantitative basis, analyzing actual buying and selling patterns of institutional investors.