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Critical Thinking mini-lesson 8

replication revisited

One of the traits of a cogent argument is that the evidence be sufficient to warrant accepting the conclusion. In causal arguments, this generally requires--among other things--that a finding of a significant correlation between two variables, such as magnets and pain, be reproducible. Replication of a significant correlation usually indicates that the finding was not a fluke or due to methodological error. Yet, I am often sent copies of articles regarding single studies and advised that it may be about time for me to change my mind on some subject. For example, I recently heard from Jouni Helminen that "It may be time to update the Skepdic website regarding magnet therapy on fibromyalgia patients." Jouni referred me to an article from the University of Virginia News. I state in my entry on magnet therapy: "There is almost no scientific evidence supporting magnet therapy." The article about a study done on magnet therapy to reduce fibromyalgia pain did nothing to change my mind. The study, conducted by University of Virginia (UV) researchers, was published in the Journal of Alternative and Complementary Medicine, which asserts that it "includes observational and analytical reports on treatments outside the realm of allopathic medicine...."

The only people who refer to conventional medicine as allopathic are rabid opponents of conventional medicine and may not be the most objective folks in the world when it comes to evaluating anything "alternative." Be that as it may, the study must stand or fall on its own merits, not on the biases of those who publish it. Furthermore, the study must be distinguished from the press release put out by UV. The headline of the UV article states that Magnet Therapy Shows Limited Potential for Pain Relief. The first paragraph states that "the results of the study were inconclusive." Not very promising. Even so, the researchers claimed that magnet therapy reduced fibromyalgia pain intensity enough in one group of study participants to be "clinically meaningful." I guess "limited potential" is the middle ground between "inconclusive" and "clinically meaningful." This is somewhat confusing.

The UV study involved 94 fibromyalgia patients who were randomly assigned to one of four groups. One control group "received sham pads containing magnets that had been demagnetized through heat processing" and the other got nothing special. One treatment group got "whole-body exposure to a low, uniformly static magnetic field of negative polarity. The other...[got]...a low static magnetic field that varied spatially and in polarity. The subjects were treated and tracked for six months."

"Three measures of pain were used: functional status reported by study participants on a standardized fibromyalgia questionnaire used nationwide, number of tender points on the body, and pain intensity ratings."

One of the investigators, Ann Gill Taylor, R.N., Ed.D. stated: "When we compared the groups, we did not find significant statistical differences in most of the outcome measures." Taylor is a professor of nursing and director of the Center for Study of Complementary and Alternative Therapies at UV. "However, we did find a statistically significant difference in pain intensity reduction for one of the active magnet pad groups," said Taylor. The article doesn't mention how many outcome measures were used.

The study's principal investigator was Dr. Alan P. Alfano, assistant professor of physical medicine and rehabilitation and medical director of the UV HealthSouth Rehabilitation Hospital. Alfano claimed that "Finding any positive results in the groups using the magnets was surprising, given how little we know about how magnets work to reduce pain." Frankly, I find it surprising that Alfano finds that surprising, since it is unlikely he would have conducted the study if he didn't think there might be some pain relief benefit to using magnets. His statement assumes they work to reduce pain and the task is to figure out how. Alfano is also quoted as saying that "The results tell us maybe this therapy works, and that maybe more research is justified. You can't draw final conclusions from only one study." Certainly, his last claim is correct. His double use of the weasel word "maybe" indicates that he realizes that you can't even make a strong claim that more research ought to be done based on the results of one study, especially if the results aren't that impressive.

Not knowing how many outcome measures the researchers used makes it difficult to assess the significance of finding one or two outcomes that look promising. Given all the variables that go into "pain" and measuring pain, and the variations in the individuals suffering pain (even those diagnosed as having the same disorder), it should be expected that if you measure enough outcomes you are going to find something statistically significant. Whether that's meaningful or not is another issue. A competent researcher would not want to make any strong causal claims about magnets and pain on the basis of finding one or two statistically significant outcomes in a study that found that most outcomes showed nothing significant.

But even if most of the outcomes had been statistically significant in this study of 94 patients, that still would not amount to strong scientific evidence in support of magnet therapy. The experiment would need to be replicated. Given the variables mentioned above, it would not be surprising if this study were replicated but found different outcomes statistically significant. Several studies might find several different outcomes statistically significant and some researcher might then do a meta-study and claim that when one takes all the studies together one gets one large study with very significant results. What you would actually get is one misleading study.

If other researchers repeat the UV study, looking only at the outcome that was statistically significant in the original study, and they duplicate the results of the UV study, then we should conclude that this looks promising. But one replication shouldn't seal the deal on the causal connection between magnets and pain relief. One lab might duplicate another lab's results but both might be using faulty equipment manufactured by the same company. Or both might be using the same faulty subjective measures to evaluate their data. Several studies that showed nothing significant for magnets and pain might be followed by several that find significant results, even if all the studies are methodologically sound. Why? Because you are dealing with human beings, very complex organisms who won't necessarily react the same way to the same treatment. Even the same person won't necessarily react the same way to the same treatment at different times.

So, a single study on something like magnets and pain relief should rarely be taken by anybody as significant scientific evidence of a causal connection between the two. Likewise, a single study of this issue that finds nothing significant should not be taken as proof that magnets are useless. However, when dozens of studies find little support that magnets are effective in warding off pain, then it seems reasonable to conclude that there is no good reason to believe in magnet therapy. And I would not give up that belief on the basis of what I read in the UV press release about their little study on magnets and fibromyalgia.

reader comments

The Univ. Virginia study sounds fairly typical of Alternative Medicine studies. Take a large number of indicators that the treatment could be effective. After the study, hunt around for one or two indicators that show effectiveness. In the "normal" curve, you can get a 2-standard-deviation effect by chance about 5% of the time. So if you have 20 indicators, you will likely find one indicator that "shows" that the treatment is effective. If you have 40 indicators, you will likely find two that indicate effectiveness. This procedure is called "data dredging," and is a definite no-no. Instead, the proper scientific procedure is to use all the data, not just those that support your pet hypothesis. "Inconclusive" is often a euphemism for "didn't work."

John W. Farley
Professor of Physics

lesson 9: straw man fallacy Last updated 12/09/10

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