Although the CIA will not acknowledge details of its

On the opposite end of the career spectrum are lumberjacks. The study shows these workers, also known as timber cutters and loggers, as having the worst occupation, because of the dangerous nature of their work, a poor employment outlook and low annual pay -- just $32,124.

New protective gear -- such as trouser covers made of fiber-reinforcement materials -- and an increased emphasis on safety have helped to reduce injuries among lumberjacks, says Paul Branch, who manages the timber department at Pike Lumber Co. in Akron, Ind. Still, accidents do occur from time to time, and some even result in death. "It's not a job everybody can do," says Mr. Branch.

But Eric Nellans, who has been cutting timber for the past 11 years for Pike Lumber, is passionate about his profession. "It's a very rewarding job, especially at the end of the day when you see the work you accomplished," he says. Mr. Nellans, 35, didn't become discouraged even after he accidentally knocked down a dead tree and broke his right leg in the process four years ago. "I was back in the woods cutting timber in five weeks," he says.

Other jobs at the bottom of the study: dairy farmer, taxi driver, seaman, emergency medical technician and roofer.

Mike Riegel, a 43-year-old roofer in Flemington, N.J., says he likes working "outside in the fresh air." Since he runs his own business, which he inherited from his father, he can start and end his day early in hot weather or do the opposite when it's cold.

The study estimates roofers earn annual incomes of $34,164, which Mr. Riegel says is consistent with what he pays new employees. Roofers also ranked poorly because of their hazardous working conditions. "You obviously can't be afraid of heights," says Mr. Riegel, who once fell two stories while working on a rooftop in the rain but luckily landed safely on a pile of soft dirt. "I missed some cement by 10 feet."

While the Defense Department has produced volumes of public reports and testimony about its detention practices and rules after the abuse scandals at Iraq's Abu Ghraib prison and at Guantanamo Bay, the CIA has not even acknowledged the existence of its black sites. To do so, say officials familiar with the program, could open the U.S. government to legal challenges, particularly in foreign courts, and increase the risk of political condemnation at home and abroad.

But the revelations of widespread prisoner abuse in Afghanistan and Iraq by the U.S. military -- which operates under published rules and transparent oversight of Congress -- have increased concern among lawmakers, foreign governments and human rights groups about the opaque CIA system. Those concerns escalated last month, when Vice President Cheney and CIA Director Porter J. Goss asked Congress to exempt CIA employees from legislation already endorsed by 90 senators that would bar cruel and degrading treatment of any prisoner in U.S. custody.

Although the CIA will not acknowledge details of its system, intelligence officials defend the agency's approach, arguing that the successful defense of the country requires that the agency be empowered to hold and interrogate suspected terrorists for as long as necessary and without restrictions imposed by the U.S. legal system or even by the military tribunals established for prisoners held at Guantanamo Bay.