Studies that have used pessimistic explanatory style as a measure of pessimism have also uncovered relations to health. Pessimistic explanatory style was associated with lower levels of two measures of cell-mediated immunity in a sample of elderly men and women (Kamen-Siegel, Rodin, Seligman, & Dwyer, 1991). A study of Harvard University graduates assessing pessimistic explanatory style at age 25 found that these men had significantly poorer health or were more likely to have died when they were assessed 20 to 35 years later (Peterson, Seligman, & Vaillant, 1988).