ABSTRACT
Researchers in most scientific fields are quite familiar with what statisticians call a "simple" interaction: a situation in which the effect of one factor upon another, or the association of one variable with another, changes at different levels of a third factor. Pharmacists and medical doctors, for example, have long realized that some combinations of drugs have synergistic effects on patients. If taken together, alcohol and barbiturates cause a much greater level of intoxication in people than would result from the additive, independent effects of the two. As another Correspondence and requests for reprints: David K. Perry, Journalism Department, Box 1482, University of Alabama, University, AL 35486.
