“What Is Lawsuit Abuse Costing Your Family?” asked a full-page ad that ran this week in several major newspapers, including The Wall Street Journal. The alleged answer: $3,520 a year.

The ad (click here), paid for by the U.S. Chamber Institute for Legal Reform, a Washington, D.C., pro-business group, also ran in the Chicago Tribune and the Washington Post, and appears on WSJ.com.

$3,250 a year? We raised our eyebrows over the number too. Fortunately, colleague Carl Bialik, aka the Wall Street Journal’s “Numbers Guy,” unpacked the figure on the Numbers Guy blog.

According to Bialik, the dollar figure comes from an annual estimate of tort costs by the Tillinghast arm of consulting firm Towers Perrin, which in turn is based on insurance data from A.M. Best. Russ Sutter, a Tillinghast principal and primary author of the study, told Bialik the firm’s numbers are being misrepresented by the U.S. Chamber Institute. According to Bialik, the ads make the dubious assumption that every lawsuit in the tort system is frivolous. Sutter said his group didn’t try to evaluate the merit of individual lawsuits, but simply set out to calculate the cost of the entire tort system.

Larry Akey, spokesman for the U.S. Chamber Institute, defended the ads and the use of the Tillinghast estimate, citing a much greater estimate of the “tort tax,” reported last year by the free-market think tank Pacific Research Institute, of $9,827 per family of four. Akey reportedly said the figure didn’t look at the cost only of abusive suits, but by choosing what he calls the “conservative” estimate from Tillinghast rather than Pacific Research Institute’s number, “we think the cost-of-abusive-lawsuit estimate is in the range we assert it to be.”

Law Blog readers, feel free to comment on the Numbers Guy blog, here.