Investment outlook among millionaires and affluent soured in February, affected by a decline in expected future household income and a drop in confidence over the economy, according to Spectrem Group, an Illinois-based research and consulting firm.

The firm announced on Wednesday that the investment outlook of households with over $1 million in investable assets dropped 10 points in February to 1, according to its Spectrem Millionaire Investor Confidence.

Investment outlook for households with over $500,000 in investable assets dropped three points to -7, according to the Spectrem Affluent Investor Confidence Index.

“The level of Millionaire investors who indicated they planned to stay on the sidelines and not invest was at its highest since September 2011,” George Walper, Jr., president of Spectrem, said in a statement.

The indices, based on 250 monthly interviews with financial decision-makers who have more than $500,000 of investable assets, are divided into five categories: A reading of 31 to 51 represents a bullish outlook, 11 to 30 mildly bullish, 10 to -10 neutral, -11 to -30 mildly bearish, and -31 to -51 bearish.

Among the factors that influenced a more bearish investment outlook, expected future household income posted the biggest decline, shaving off 11.07 points for a reading of -9.51, an almost four-year low. Confidence in the Economy also dropped 4.14 points to -6.95.

Investment preferences for affluent investors also saw a shift from last month.

The most active investment instrument was stock mutual funds, which posted an increase of 4.36 from last month to reach 31.3 points, a six-month high.

This was followed by stocks (28.2 points), cash (18.3 points), bond mutual funds (15 points), real estate (11.3) and bonds (7.1).

Among millionaire investors, stock mutual funds (32.5 points), stocks (30.2 points) and cash (21 points) were the three most popular investment vehicles in February.

Despite bullish readings in the top three investment preferences, all represent a decline from last month.