Investor confidence among millionaires rose to its highest level in more than two years as optimism about the economy increased.

The Spectrem Millionaire Investor Confidence Index rose five points this month to negative-one, according to a monthly survey by Spectrem Group, a Chicago research firm, that was released Wednesday. This is the ninth-consecutive neutral reading and the highest level for the index since December 2007 when it stood at eight.

Meanwhile, the Spectrem Affluent Investor Confidence Index, which measures the investment confidence and outlook of households with $500,000 or more in investable assets, rose three points in April to negative-nine. This neutral reading is the index’s highest since December 2007, when it stood at zero.

George H. Walper Jr., Spectrem’s president, said that the surge in the Dow Jones Industrial Average this month “was clearly a positive for the nation’s wealthiest investors. However, the outlook of both groups remains neutral with some lingering uncertainty about the economy – specifically, unemployment levels.”

In response to an open-ended question about the one factor most affecting their investment plans, affluent investors in April cited: stock market conditions (21%); the economic environment (16%); household cash flow (8%); household income (7%); retirement (7%) and the political climate (4%). Those choosing stock market conditions fell from 22% in January, the last time this question was asked, and those citing the economy fell from 20%.

Millionaires were slightly more focused on the economy (21%) than the affluent but less focused on stock market conditions (20%).