In 1948, Betz and Thomas classified 45 Johns Hopkins medical students in three personality groups on the basis of psychological tests and questionnaires. The students were listed either as "alphas," described as cautious, reserved, quiet and undemanding; "betas," spontaneous, active and outgoing; or "gammas," moody, emotional and either over- or under-demanding.

Thirty years later, Betz and Thomas looked at the health records of the former students. They found that 77.3 percent of the gamma group suffered from major disorders, including cancer, high blood pressure, heart disease and emotional disturbances. The incidence of disorders was only 25 percent in the alpha group and 26.7 percent in the betas. The doctors repeated the study on another group of 127 male students from the classes of 1949 through 1964 with similar results. "Too often, gamma people get lost in their own emotions," says Betz. "While a person's temperament cannot be changed, more support from outside sources such as more human contacts might help lessen a gamma's risk of disease."