ABSTRACT

The use of analysis of variance to test for the overall significance of a set of means when participants have been classified in only one way. In a two-way analysis of variance, is known as a main effect. Often, however, researchers use a two-way classification, such as which drug was taken and how long participants have been depressed. Each way in which participants are classified yields a main effect in analysis of variance. Because participants were also classified in terms of their length of depression, there is a main effect for short-term versus long-term depression, which can be seen by examining the row means of 8.22 and 6.56. This main effect indicates that, overall, those with short-term depression were less depressed at the end of the experiment than those with long-term depression.