Each CEO is rated in several categories, including "Market Value/Invested Capital," a measurement of how investors value the company's assets relative to their cost; the average of the company's last three years' economic margin scores; the change to the economic margin in the past year; and a management quality score. All four scores were calculated from Applied Finance Group's proprietary metrics.

Ballmer's ranking fell dramatically in the latest index, dropping to No. 73 from 2009's No. 8.

The WCI gave and Ballmer an "F" in the economic margin change from 2009 to 2010, meaning that the company was in the bottom 20% of the 500 evaluated. Microsoft was awarded an "A" in management quality, however.

Forty-five CEOs out of the 500 assessed by the WCI fell even further than Ballmer, including Marc Benioff of customer relationship management (CRM) provider Salesforce.com, who dropped 75 places to No. 105; and John Riccitiello, the CEO of game maker Electronic Arts (down 90 spots to No 261).

Helm defended Microsoft's performance.