Prayer: Provable?

The observation is often made that God seems to only grant prayers for things that had a chance to happen on their own anyway. He'll cure a temporary disease, put the odd cancer into remission, let someone win a sports match, etc. He never does anything truly miraculous that would defy our current knowledge of biology and physics--like regenerate a lost limb, regrow an eye, bring someone back from the dead, or really anything that would prove beyond a doubt that supernatural intervention has taken place. Everything He allegedly does could have happened by chance, anyway. People have argued against this, saying that such events have taken place, as recorded in the bible... but treating the bible as an accurate historical record is another issue altogether (perhaps for another post).

The question now is, does prayer give people a statistically better chance of having these kinds of things happen for them? For example, of all the small percentage of people who have cancer that goes into remission, did most of them pray to God? Of all the cancer patients who died from the disease, did most of them not pray? Presumably, this should be something that science can test. And it has.

When looking around for the results of "prayer experiments," you will tend to run in to conflicting information. The Wikipedia has a section on experimental evaluation of prayer here that references a number of different studies with varying results.

I did a quick search on PubMed for "intercessory prayer," and found 66 articles. There were a few that detailed studies that claim to produce positive results:

Positive therapeutic effects of intercessory prayer in a coronary care unit population.
Byrd RC, 1988

The control patients required ventilatory assistance, antibiotics, and diuretics more frequently than patients in the IP group. These data suggest that intercessory prayer to the Judeo-Christian God has a beneficial therapeutic effect in patients admitted to a CCU.

A closer analysis of this study can be found here. Many problems with this study can be pointed out. The main problem is that the very thing they purported to test--prayer--was not controlled for. Byrd himself admitted that there was nothing stopping the friends and family members of people in the control group from praying for them. Essentially there was no way to know for sure that the prayer group was actually receiving more prayers than the control group.

The big problem, however, is that out of the 29 variables measured, only six seemed to be significantly different between the two groups. Byrd himself admitted that, due to the number of variables being considered, these differences on their own could not be considered to be statistically significant--it is only after applying severity scores and multivariate statistics that the differences become significant. The problem with that is the six variables were related to one another, meaning the methods used to obtain significance may be misleading. To quote the critique linked above:

One must note the interrelationships among these six categories: for instance, the development of congestive heart failure automatically leads to the need for diuretics; the development of pneumonia automatically requires the use of antibiotics; and the development of either would likely increase the risk of developing the other, of requiring intubation or ventilation, and of suffering cardiopulmonary arrest. Thus, the development of any single complication may automatically lead to a cascade of other complications and therapeutic interventions that cannot be considered independent events, rendering the significance of Byrd's data highly doubtful.

These problems with the methods used means that this study should be viewed skeptically, until its results have been independently replicated in similar experiments.

Other references regarding the Byrd study:
Science of Prayer Reality Check
Intercessory Prayer - Does it Work?

A randomized, controlled trial of the effects of remote, intercessory prayer on outcomes in patients admitted to the coronary care unit.
Harris WS, Gowda M, Kolb JW, Strychacz CP, Vacek JL, Jones PG, Forker A, O'Keefe JH, McCallister BD, 1999

OBJECTIVE: To determine whether remote, intercessory prayer for hospitalized, cardiac patients will reduce overall adverse events and length of stay.
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CONCLUSIONS: Remote, intercessory prayer was associated with lower CCU course scores. This result suggests that prayer may be an effective adjunct to standard medical care.

An analysis of this study and its similarities and differences to the Byrd study that was published in the Scientific Review of Alternative Medicine can be found here. Essentially, this study strived to replicate the findings of the Byrd study, but failed to do so--using Byrd's analysis methods failed to find any significant difference between the IP and control groups. They did create their own scoring system, however, which gave the IP group an 11% higher score (with a 1/25 possibility of being attributable to random chance). As with the Byrd study, this one fails to offer any compelling evidence to support the conclusions. Further testing and replication should be required.

Other references regarding the MAHI study:
Intercessory Prayer and Patient Outcomes in Coronary Care Units
Efficacy of Prayer

Does prayer influence the success of in vitro fertilization-embryo transfer? Report of a masked, randomized trial.
Cha KY, Wirth DP, 2001

OBJECTIVE: To assess the potential effect of intercessory prayer (IP) on pregnancy rates in women being treated with in vitro fertilization-embryo transfer (IVF-ET).
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CONCLUSION: A statistically significant difference was observed for the effect of IP on the outcome of IVF-ET, though the data should be interpreted as preliminary.

This was a highly controversial study that has become very suspect under subsequent scrutiny. this article on the-scientist.com details some of the controversy. Ultimately, the credibilities of the study and the people involved in it are poor, and its results would need to be reproduced before they should be taken seriously.

Other references about the IVF-ET study:
The Columbia University 'Miracle' Study: Flawed and Fraud
Follow-up to the above: The Bizarre Columbia University 'Miracle' Saga Continues
Faith Healing by Prayer: Review of a Questionable Study

Effects of remote, retroactive intercessory prayer on outcomes in patients with bloodstream infection: randomized controlled trial.
Leibovici L, 2001

OBJECTIVE: To determine whether remote, retroactive intercessory prayer, said for a group of patients with a bloodstream infection, has an effect on outcomes.
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CONCLUSION: Remote, retroactive intercessory prayer said for a group is associated with a shorter stay in hospital and shorter duration of fever in patients with a bloodstream infection and should be considered for use in clinical practice.

The very idea of this study is quite controversial--that prayer can have a retroactive effect on an event that occurred up to 10 years in the past. Many responses were sent in to the publication regarding this paper, which can be read here. A few poignant observations made by readers:

There was no significant difference between the two groups with regards to the most clinically important outcome (mortality), and the median values varied little between prayer and non-prayer on both length of stay (7 and 8 days) and fever duration (2 days each).

The data on the the most significant finding,length of stay, appears to be skewed by a few abnormally high results in the control group.This is demonstrated by the fact that the median length of stay is the same in both groups but the maximum length of stay in the control group is twice that in the intervention group. This may represent a type I statistical error,despite the large sample size. From a cynical stand point, it is a shame that God cannot save your life but might get you out of hospital a few days earlier.

It is pretty much given that a study with findings such as this would cause an uproar in the scientific community, but regardless, they do seem to make the salient point that the apparent positive results of the study seem to be more due to a statistical anomaly, as opposed to divine intervention.

Intercessory prayer in psychological well-being: using a multiple-baseline, across-subjects design.
Tloczynski J, Fritzsch S, 2002

This study involved a group of students taking regular anxiety evaluation tests in order to measure the effect that prayer had on their anxiety. The results do seem to indicate that there is some psychological benefit to knowing that you are being prayed for, but does not indicate any kind of supernatural power in prayer.

The bulk of the studies generally seem to point to the same conclusions. Namely, the only benefits that prayer can have are psychological and emotional ones (generally only if the subject believes in prayer, and believes that he or she is being prayed for). These results also appear true for belief in other forms of alternative medicine as well, such as therapeutic touch or meditation. The evidence, however, supporting the divine intervention of God in situations where prayer is being used, is underwhelming to the point of non-existence.

Following are some of the many other studies that involve testing the efficacy of prayer:

Complementary healing therapies.
Wirth DP, Barrett MJ, 1994

The effect of non-contact therapeutic touch (NCTT) in isolation and in combination with Reiki, LeShan, and Intercessory Prayer on the healing rate of full thickness human dermal wounds was examined utilizing a randomized, double-blind, within subject, crossover design.
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Results showed significance for the treated versus the control group but in the opposite direction from that expected. Several factors could have contributed to the nonsignificance obtained including: (a) the natural healing ability of the two mimic practitioners; (b) the subjects' increased proficiency with the self-regulatory techniques; and (c) a carryover effect from the two NCTT healers and/or the Reiki, LeShan, or Intercessory Prayer healers.

Interestingly, this study showed the alternative methods of healing (such as prayer) actually produced negative effects on healing.

An experimental study of the effects of distant, intercessory prayer on self-esteem, anxiety, and depression.
O'Laoire S, 1997

Improvement on all II measures was significantly related to subjects' conviction concerning whether they had been assigned to a control or an experimental group. Possible explanations include the placebo/faith effect, the time displaced effect, and extraneous prayer.

This one seems to have found that one only needs to believe that they are being prayed for in order to improve in the areas being measured, and that the actual prayers made no difference.

Intercessory prayer in the treatment of alcohol abuse and dependence: a pilot investigation.
Walker SR, Tonigan JS, Miller WR, Corner S, Kahlich L, 1997

OBJECTIVE: To conduct a pilot study of the effect of intercessory prayer on patients entering treatment for alcohol abuse or dependence.
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CONCLUSION: Intercessory prayer did not demonstrate clinical benefit in the treatment of alcohol abuse and dependence under these study conditions. Prayer may be a complex phenomenon with many interacting variables.

Intercessory prayer for the alleviation of ill health.
Roberts L, Ahmed I, Hall S, 2000

OBJECTIVES: To review the effectiveness of prayer as an additional intervention for those with health problems already receiving standard medical care.
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MAIN RESULTS: There was no evidence that prayer affected the numbers of people dying from leukaemia or heart disease...

Effects of intercessory prayer on patients with rheumatoid arthritis.
Matthews DA, Marlowe SM, MacNutt FS, 2000

RESULTS: Patients receiving in-person intercessory prayer showed significant overall improvement during 1-year follow-up. No additional effects from supplemental, distant intercessory prayer were found. CONCLUSIONS: In-person intercessory prayer may be a useful adjunct to standard medical care for certain patients with rheumatoid arthritis. Supplemental, distant intercessory prayer offers no additional benefits.

So, again, people who knew they were being prayed for showed improvement, but the remote prayers made no difference. Proof of God's intervention? Or something more mundane like the placebo effect?

The effects of intercessory prayer, positive visualization, and expectancy on the well-being of kidney dialysis patients.
Matthews WJ, Conti JM, Sireci SG, 2001

OBJECTIVE: To explore the effect of intercessory prayer, positive visualization, and outcome expectancy on a wide range of medical and psychological measures in critically ill patients.
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CONCLUSIONS: The effects of intercessory prayer and transpersonal positive visualization cannot be distinguished from the effect of expectancy. Therefore, those 2 interventions do not appear to be effective treatments.

Intercessory prayer and cardiovascular disease progression in a coronary care unit population: a randomized controlled trial.
Aviles JM, Whelan SE, Hernke DA, Williams BA, Kenny KE, O'Fallon WM, Kopecky SL, 2001

OBJECTIVE: To determine the effect of intercessory prayer, a widely practiced complementary therapy, on cardiovascular disease progression after hospital discharge.
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CONCLUSIONS: As delivered in this study, intercessory prayer had no significant effect on medical outcomes after hospitalization in a coronary care unit.

Pilot study investigating the effect of intercessory prayer in the treatment of child psychiatric disorders.
Mathai J, Bourne A, 2004

OBJECTIVE: To investigate whether intercessory prayer had an effect on the outcomes of a group of children with psychiatric conditions, using a triple blind randomized study design. CONCLUSION: This study was unable to show any additional benefits for patients who received intercessory prayer compared to those who received treatment as usual.

Music, imagery, touch, and prayer as adjuncts to interventional cardiac care: the Monitoring and Actualisation of Noetic Trainings (MANTRA) II randomised study.
Krucoff MW, Crater SW, Gallup D, Blankenship JC, Cuffe M, Guarneri M, Krieger RA, Kshettry VR, Morris K, Oz M, Pichard A, Sketch MH Jr, Koenig HG, Mark D, Lee KL, 2005

INTERPRETATION: Neither masked prayer nor MIT therapy significantly improved clinical outcome after elective catheterisation or percutaneous coronary intervention.

Study of the Therapeutic Effects of Intercessory Prayer (STEP) in cardiac bypass patients: a multicenter randomized trial of uncertainty and certainty of receiving intercessory prayer.
Benson H, Dusek JA, Sherwood JB, Lam P, Bethea CF,
Carpenter W, Levitsky S, Hill PC, Clem DW Jr, Jain MK, Drumel D, Kopecky SL, Mueller PS, Marek D, Rollins S, Hibberd PL, 2006

BACKGROUND: Intercessory prayer is widely believed to influence recovery from illness, but claims of benefits are not supported by well-controlled clinical trials. Prior studies have not addressed whether prayer itself or knowledge/certainty that prayer is being provided may influence outcome.
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CONCLUSIONS: Intercessory prayer itself had no effect on complication-free recovery from CABG, but certainty of receiving intercessory prayer was associated with a higher incidence of complications.

Again, a study that oddly associates receiving prayers with negative effects.

The efficacy of distant healing for human immunodeficiency virus--results of a randomized trial.
Astin JA, Stone J, Abrams DI, Moore DH, Couey P, Buscemi R, Targ E, 2006

The purpose of this study was to examine the potential efficacy of distant healing in a population of patients with human immunodeficiency virus (HIV)/aquired immune deficiency syndrome (AIDS).
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CONCLUSIONS: Distant healing or prayer from a distance does not appear to improve selected clinical outcomes in HIV patients who are on a combination antiretroviral therapy.