One screams and throbs at the camera, while the other would address his viewers with the wooden calm of an English gentleman.

Yet despite the Jekyll-and-Hyde differences between Jim Cramer and the late Louis Rukeyser, there's one notable similarity between their TV programs: Any mention of a company could move its stock.

This is a crucial fact for individual investors to understand, because the stock market is a crafty place where the smart money loves to prey on predictable patterns like the instant bounce for stocks touted by Cramer on CNBC's Mad Money program. And when the pros win, the ordinary folk are bound to lose.

Cramer fans needn't despair. Rather than swearing off the former hedge fund manager's advice, all that may be required is the poise and patience to wait a couple of weeks before putting your money where his mouth is, judging from a study into trading patterns after each airing of Mad Money on weekday nights. Cramer urges viewers to avoid the temptation to rush right in, especially during after-hours trading.

It's rare for average investors to have direct access to a professional stock picker with Cramer's knowledge and experience.

There was a time, before the Internet, where it was hard to get stock and bond quotes, let alone timely advice from the pros. One easily accessible resource was the weekly edition of Barron's. Even more accessible was Rukeyser's long-running Wall Street Week, which appeared once a week, free of charge, on PBS.

Since Barron's came out on the weekend and Rukeyser's show generally ran on Friday nights, there was an entire weekend to mull the information imparted by the money managers and investment analysts.

The pace has quickened dramatically since the mid '90s, stoked by all-day market coverage and prognostication on CNBC, Web sites and frothy online message boards.

With a stream of stock tips as steady and high-profile as Cramer's, it doesn't take technology to see there's a pattern to exploit. So for better or worse, it seems the pros are scoping out the joint when it comes to Mad Money, judging from an academic study into trading after each edition of program.

The study by Joseph Engelberg, Caroline Sasseville and Jared Williams - doctoral students at the Kellogg School of Management at Northwestern University - tracked the performance of about 250 companies that drew a favorable mention on Cramer's evening program between late July and mid October last year.

Shares of the recommended companies outperformed the market by an average of 3.5 percent on the first day after Cramer's tout. The smallest companies outperformed by 6.2 percent on average.

Almost immediately, however, the stocks beat a hasty retreat, surrendering the initial gains within about 12 days. In tandem with this activity, the researchers found a sharp uptick in opportunistic behavior among short-sellers, who sell borrowed shares with plans to buy them back at a lower price later.

Bruce Meyerson is a national business columnist for the Associated Press. Write to him at bmeyerson@ap.org.