To a non-expert, it looks like studies on prayer are a mixed bag. This meta-analysis found no effect: http://link.springer.com/article/10.1207/s15324796abm3201

To a non-expert, it looks like studies on prayer are a mixed bag. This meta-analysis found no effect: http://link.springer.com/article/10.1207/s15324796abm3201_3#page-1 http://link.springer.com/article/10.1207/s15324796abm3201_3#... But this one did: http://rsw.sagepub.com/content/17/2/174.short http://rsw.sagepub.com/content/17/2/174.short Another interesting study: http://online.liebertpub.com/doi/abs/10.1089/1075553041323803 http://online.liebertpub.com/doi/abs/10.1089/107555304132380... ("No direct intervention effect on the primary outcomes was found. A marginally significant reduction in the amount of pain was observed in the intervention group compared to controls. The amount of concern for baseline problems at follow-up was significantly lower in the intervention group when stratified by subject's baseline degree of belief that their problem could be resolved. Prayer intervention appeared to effectively reduce the subject's level of concern only if the subject initially believed that the problem could be resolved. Those in the intervention group who did not believe in a possible resolution to their problem did not differ from controls. Better physical functioning was observed in the intervention group among those with a higher belief in prayer and surprisingly, better mental health scores were observed in the control group with lower belief in prayer scores.")