test for contrasts
any procedure used to determine which of the specific groups examined in an analysis of variance are significantly different from each other, whether this takes the form of a post hoc comparison carried out after the data have been observed or an a priori comparison formulated before observation. For example, suppose one wished to analyze the outcomes from three different modes of training: (a) video-based instruction, (b) live lecture by an instructor, and (c) text reading only. After conducting an analysis of variance and obtaining results indicating there is a significant difference between the three modes, one could use a test for contrasts to evaluate various combinations of modes to identify where exactly the differences lie. Examples of specific tests for contrasts include the Scheffé test, Tukey’s honestly significant difference test, and the Fisher least significant difference test.