The Spectrem Affluent Investor Confidence Index released Wednesday showed that affluent households’ confidence in the U.S. economy plunged 11 points in June to a reading of minus 9—its biggest drop in more than three years.

The decline is the largest since January 2008 for the affluent index, which measures the investment confidence and outlook of households with $500,000 or more in investable assets, according to Chicago-based Spectrem Group

The index now stands at its lowest level since October 2010, when it stood at minus 13.

In addition, the Spectrem Millionaire Investor Confidence Index dropped 2 points in June to minus 1.

“Affluent investors posted their biggest decline in investment confidence in more than three years in June, with millionaires’ confidence falling slightly as well,” said George H. Walper Jr. (left), president of Spectrem Group, in a statement. “The nation’s wealthiest investors overwhelmingly cited the economy as their biggest concern. Given the worrisome economic news that emerged in June, it’s not surprising to see wealthy Americans struggling with their investment optimism.”

In response to an open-ended question about the most serious threat to achieving their financial goals, affluent investors in June cited the economy (35%), the political climate (14%), market conditions (13%), inflation (9%), unemployment (7%) and health (1%). Those citing the economy rose from 22% in March, the last time the question was asked, while those citing the political climate fell from 22%.

Millionaires were less focused on the economy (28%) than the affluent, but more focused on market conditions (19%).

Additional data from both indexes are available on Spectrem’s Millionaire Corner website.

Meanwhile, on Tuesday the Conference Board's June index of overall U.S. consumer confidence fell to 58.5 from 61.7 in May, below the 61.0 consensus, for a seven-month low. The present situation index decreased to 37.6 from 39.3, and the expectations index declined to 72.4 from 76.7.

Most of the decline was due to a 4.3-point decline in the expectations index, which is largely driven by stock and gasoline prices, according to Ian Shepherdson, chief U.S. economist for High Frequency Economics Ltd., in Valhalla, N.Y.

“Gas prices have dropped, but so have stock prices, and for now the latter seems to be having a greater impact,” Shepherdson said in an analyst's note. “We expect this to reverse over the next couple of months, and we think both the expectations and headline indexes will be much stronger by the end of the summer.”

Read about last month’s Spectrem indexes at AdvisorOne.com.