Confidence among high-net-worth investors tumbled in August, according to a monthly survey by Spectrem Group.

The Spectrem Affluent Investor Confidence Index declined four points, to a "mildly bearish" minus-20, and the Spectrem Millionaire Investor Confidence Index declined 11 points, to minus-18.

The decline in the millionaire index returned it to "mildly bearish" territory after 12 straight months in "neutral," according to Chicago-based Spectrem.

"The millionaires' decline is particularly troubling since it suggests millionaires, typically more sophisticated than the broader affluent population, are reverting to a bearish frame of mind," said George H. Walper Jr., Spectrem's president.

The Spectrem Affluent Investor Confidence Index is based on 250 monthly interviews with households with $500,000 or more in investable assets. The Spectrem Millionaire Investor Confidence Index is based on a subset of the overall group.

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