To find the answer, Ziobrowski recruited three other professors, including his wife, Brigitte, who oversaw the tedious process of actually turning the entries on the opaque disclosure forms into usable data. While the House forms were available in libraries, getting the records from Senate offices proved especially difficult. “We finally had to buy many of them at 20 cents a page,” Ziobrowski told me. And even after they got the forms, “it took years to go through and track all of those transactions,” Ziobrowski says.

Their results were necessarily approximate. Some members left office before selling shares; others would sell some, but not all, of their stock. “And then there are others who just don’t bother to tell you when they sell,” Ziobrowski told me. “You’ll see the portfolio change, but you don’t know why. There’s no watchdog, there’s no one who audits to check that they’re accurate.”

Even so, the professors eventually had a data set comprising all known senatorial transactions between 1993 and 1998. And what they found shocked Ziobrowski.

“Most of the time, you do studies like this, and you end up concluding that there are no abnormal returns. Call us naive, but the part that bothered me most about Boller’s work is that it suggests that they’re doing something sneaky, but it didn’t actually show that they were doing anything sneaky.” He chuckled. “None of us were betting our tenure on the results of this study.”

But when they’d completed their analysis, it looked like they—and at least a few members of Congress—had hit the jackpot. Their analysis of the Senate returns over the six-year period, published in the Journal of Financial and Quantitative Analysis in 2004, showed that the Senate portfolio outperformed the market by approximately 12 percent a year. In April of this year, the team published a follow-up analysis of the House in Business and Politics, which showed that House members on average outperformed the market by a smaller but still impressive figure—roughly 6 percent a year.

These numbers are bigger than they sound. If you took $100 and invested it at 6 percent over a 40-year career, when you retired, that $100 would have increased almost tenfold … while if your portfolio averaged a steady 12 percent, your original $100 would have turned into more than $8,000. If you’ve looked at your 401(k) recently, you know most people don’t get such returns. And that was just the extra profits they made, over and above the 20 percent annual return that even a blind monkey with a dartboard and an E*Trade account was making back in the late 1990s. A study of corporate insiders, who presumably have lots of information about their firm’s performance, showed that their purchases earned abnormal returns of only about 6 percent a year. Senators seemed to be the greatest stock pickers since Warren Buffett.