The study was designed as a randomized and blinded trial, meaning that most patients did not know whether someone was praying for them or not. Such trials are considered the gold standard for scientific proof.
More than 1,800 patients were divided into three groups: those who were told someone was praying for them; those who were told only that someone might pray for them and got prayers; and those who were told someone might pray for them but received no prayers. About 65% of the patients said they strongly believed in the power of prayer.
Two Catholic monasteries and one Protestant group offered the prayers. They were given patients' first names and the first initial of their last names. The groups started praying the night before surgery and continued for two weeks.
All members of the prayer groups recited the same intercession, asking for "a successful surgery and a quick, healthy recovery and no complications."
Researchers said they didn't ask family members of the sick people to stop praying because it would have been unethical to do so, meaning some people received more prayers than others.
The results showed that prayers had no beneficial effect on patients' recovery 30 days after surgery. Overall, 59% of patients who knew they were being prayed for had complications, compared to 51% of the patients who did not receive prayers. The difference was not considered statistically significant.
Atrial fibrillation, a fluttering of the heart that can be related to stress, was the most common complication in all groups but was more likely to occur among patients who knew others were praying for them.
All groups were just as likely to develop infections or die.
"We conclude that telling people introduces the stress response," said Dr. Charles Bethea of Integris Baptist Medical Center in Oklahoma City and a study researcher.
He surmised that patients thought, "Am I so sick that they had to call in the prayer team?"
Dr. Richard P. Sloan, a professor of behavioral medicine at Columbia University School of Medicine, who was not involved in the research, said the study underscored the futility of trying to measure the power of prayer.
One problem in the study, he said, was that in addition to the organized prayer, some patients prayed for themselves and received prayers from families, friends, people they work with or their congregations.
"They have absolutely no idea how much prayer individuals in any of the groups received," Sloan said. "If we can't know that, we can't draw any conclusions whatsoever about the intervention."
Bob Barth of Silent Unity, the prayer organization in Lee's Summit, Mo., that was the Protestant group involved in the study, said the results didn't shake his confidence in prayer. "People of faith don't need a prayer study to know that prayer works," he said.
But Koenig said clinical trials would never answer that question. "Science is powerful and wonderful in determining the orbit of the Earth, the speed of a bullet, the power of a new drug. But now we've asked science to study something that occurs outside of space and time.
"This shows you shouldn't try to prove the power of the supernatural," he said.
