Global investor confidence has returned to levels of last summer, according to a State Street index, in what is the second indication of optimism in the world markets in a little over a week, with North American investors in particular showing increased risk appetite.

State Street's Investor Confidence Index, which measures investors' exposure to equities, rose 9.4% to 79.6, the highest figure since July last year. The figure is up from a one year low of 48.2, measured six months ago.