Spectrem Group said its millionaire index of investor confidence posted its largest-ever gain last month.

The Chicago research firm said last week that its Millionaire Investor Index rose 16 points from November, to negative-23.

The Standard & Poor's 500 Index rose 0.8% in December after fall 5% in November leaving the index down 38.5% for the year.

The Spectrem index, which was established in February 2004, reached a record low of negative-39 in November, and last month's gain returned it to mildly bearish territory, Spectrem said.The largest previous gain was 13 points in November 2005.

The Spectrem Affluent Investor Index, which measures the investment outlook of households with more than $500,000 of investable assets, rose 8 points, to negative-31, remaining in bearish territory. It also had reached a record low in November.

Spectrem asked affluent investors an open-ended question last month about the most serious threat to achieving their financial goals. The most common response was the economy (28%), followed by market conditions (19%), unemployment (15%), the political climate (8%), health-related issues (3%), and housing and real estate (1%).

In September, the last time this question was asked, 38% of affluent investors chose the economy. When asked the same question last month, 30% of millionaires selected the economy, and 16% chose market conditions.

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