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Finding the Right Comparison Group

Sometimes, finding the right comparison group can make a crucial difference in a research study—and in peoples' lives. In the 1980s, psychiatrists in Israel began to see patients who fell into trance-like states, spoke "in tongues," and made strong, rapid head movements (Witztum et al., 1996). Many of these patients also behaved strangely or aggressively, or sat listlessly and refused to eat. At first, psychiatrists tried to treat these patients with anti-psychotic drugs or long hospitalizations, with no success.

The psychiatrists failed because they compared these patients' symptoms only with the behavior of other Israeli patients. In fact, the new disorder's victims were Ethiopian Jews who had recently immigrated to Israel. The patients saw themselves as suffering from possession by a Zar, an evil spirit well-known to Ethiopians, which attacks victims who are suffering psychological stress. When the patients reduced their stress by gaining support from family members and performing traditional Ethiopian ceremonies to please the Zar, they recovered.