I've spent the last eight years asking that question. Having satisfied myself—if not everyone I've met—that there's value in using empirical methods to study prayer, I've thought a lot about how to do it.

My research has taken me all over the United States, and to Canada, Brazil, and Mozambique. I've watched how people in different cultures pray for healing—who does it, what they say, what they do with their bodies, what they say they experience. And I've examined before-and-after medical records and written surveys; used medical equipment to test people's hearing and vision before and after prayer; and done follow-up interviews that span eight years.

There are some who argue that scientists have no business studying prayer. What the late Stephen Jay Gould called the "nonoverlapping magisteria" of science and religion must be kept distinct. I believe that it is possible to respect the boundaries separating religion from science while asking empirical questions about prayer and health. And the fact is that people do pray for their health, whether or not their physicians approve. If prayer practices can affect health-for better or for worse-it seems to me that doctors, patients, and policymakers should all want to know. Once we have a clearer answer to the questions of whether and in what direction prayer affects health, we can look more closely at possible mechanisms.

I am not suggesting that scientific testing can prove or disprove that "God" exists or answers prayer, or that the "healing power of prayer" is or is not real. But it is possible to study how people understand and practice prayer and to measure certain effects of prayer on health. This to me seems like exactly the kind of project that scientists should be eager to undertake.