What the doctors measured were the number of complications post-surgery (the Society of Thoracic Surgeons has defined these complications in a reasonably precise way). It is here that the study becomes interesting. What the Benson team found was that the least number of complications occurred in the group of patients who were not prayed for and were ignorant of that fact (Group 2). The largest number of complications occurred in the group of patients who were prayed for and were aware of that fact (Group 3). In the figure, the red arrows show the direction of increasing risk.
The results are statistically significant; that is, it is unlikely these numbers could've been obtained by pure chance. Benson et al., are strangely reluctant to make this conclusion. In their words:
We have no clear explanation for the observed excess of complications in patients who were certain that intercessors would pray for them (group 3)... the excess may be a chance finding.
But, in an otherwise laudatory review, the lead editorial in the same issue of the American Heart Journal heaped scorn on this pusillanimity:
While presenting these results clearly and noting them in discussion, the investigators take an almost casual approach towards any explanation, stating only that it “may have been a chance finding.” It is rather unusual to attribute a statistically significant result in the primary end point of a prospective, multicenter randomized trial to “chance.” If the results had shown benefit rather than harm, would we have read the investigators' conclusion that this effect “may have been a chance finding” with absolutely no other comments, insight, or even speculation? [Amer. Heart J. 151(4). pp. 762-764].
They go on to argue that cultural biases should not stand in the way of studying religious phenomenon. They're absolutely right. Religion is not within the purview of science. But religious claims are. It's an idea that has been gaining steam in recent years. Generally, scientists have held back, been apologetic for negative results, and avoided confrontation. It'd be interesting to see if Medicine becomes the new villain in the minds of the faithful; Evolution now bears the brunt of the animus.