EXAMPLE 3 Pig whipworms and the need for further study

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Crohn’s disease is a chronic inflammatory bowel disease. An experiment reported in Gut, a British medical journal, claimed that a drink containing thousands of pig whipworm eggs was effective in reducing abdominal pain, bleeding, and diarrhea associated with the disease.

Experiments that study the effectiveness of medical treatments on actual patients are called clinical trials. The clinical trial that suggested that a drink made from pig whipworm eggs might be effective in relieving the symptoms of Crohn’s disease had a “one-track” design—that is, only a single treatment was applied:

Impose treatment → Measure response

Pig whipworms → Reduced symptoms?

The patients did report reduced symptoms, but we can’t say that the pig whipworm treatment caused the reduced symptoms. It might be just the placebo effect. A placebo is a dummy treatment with no active ingredients. Many patients respond favorably to any treatment, even a placebo. This response to a dummy treatment is the placebo effect. Perhaps the placebo effect is in our minds, based on trust in the doctor and expectations of a cure. Perhaps it is just a name for the fact that many patients improve for no visible reason. The one-track design of the experiment meant that the placebo effect was confounded with any effect the pig whipworm drink might have.

The researchers recognized this and urged further study with a better-designed experiment. Such an experiment might involve dividing subjects with Crohn’s disease into two groups. One group would be treated with the pig whipworm drink as before. The other would receive a placebo. Subjects in both groups would not know which treatment they were receiving. Nor would the physicians recording the symptoms of the subjects know which treatment a subject received so that their diagnosis would not be influenced by such knowledge. An experiment in which neither subjects nor physicians recording the symptons know which treatment was received is called double-blind.