Insider trading?

US senators' personal stock portfolios outperformed the market by an average of 12 per cent a year in the five years to 1998, according to a new study.

"The results clearly support the notion that members of the Senate trade with a substantial informational advantage over ordinary investors," says the author of the report, Professor Alan Ziobrowski of the Robinson College of Business at Georgia State University.

There was no difference in performance between Democrats and Republicans.

A separate study in 2000, covering 66,465 US households from 1991 to 1996 showed that the average household's portfolio underperformed the market by 1.44 per cent a year, on average. Corporate insiders (defined as senior executives) usually outperform by about 5 per cent.