Jane Jacobs tells a story about a handed-down meatloaf recipe: After the loaf is made, the end is cut off. “Why?” she asked. “We’ve always done it that way,” she was told. The original recipe was for a smaller oven, it turned out; the end was cut off to make the loaf fit in the oven.

I thought of this story when I read a recent study in the Annals of Internal Medicine that compared three treatments for back pain: acupuncture, “sham acupuncture,” and “conventional therapy.” Sham acupuncture was like acupuncture except that the needles were put in “wrong” places, inserted less deeply, and not rotated after insertion. Conventional therapy was drugs, physical therapy, and exercise. The study found that acupuncture and sham acupuncture were equally effective. Both were much better than conventional therapy. The results imply that acupuncture works, but the surrounding theory (meridians, etc.) is wrong. Which I find reassuring.

Psychotherapy is essentially the same. Lots of studies show that psychotherapy helps — but many studies also imply that the surrounding theory is wrong. Untrained therapists are as effective as trained therapists. Keeping a journal has similar effects. The active ingredient may be telling your problems, just as the active ingredient of acupuncture is apparently needle insertion.

Ritual — doing something just because — can be found in meatloaf recipes, acupuncture, psychotherapy, and clinical trials. In the discussion section of the acupuncture paper, the authors wrote:

Potential limitations of this study [include] inability to blind acupuncturists to the form of acupuncture.

Just as the meatloaf cooks did not understand their recipe, the acupuncture researchers did not understand their research design. The original reason for blinding was to equate expectations. That the two forms of acupuncture came out equal in spite of unequal expectations among the therapists is better evidence that expectations were not important. The authors failed to grasp that lack of blinding worked in their favor.

Thanks to Hal Pashler.