One-Way Designs with Quantitative Factors

In some designs, meaningful numerical values can be assigned to the factor levels. An example of this might be a study of extinction (i.e., “unlearning”) of a learned response after 10, 20, 30, 40, 50, and 60 learning trials. The six numbers of learning trials are the six levels of the factor being studied; the data are the numbers of trials to extinction. The labels on the factor levels in this experiment are meaningful numerical values: Thirty trials are 20 more than 10, 60 are 40 more than 20, and so on. If the cell means from such an experiment were plotted in a graph, they might look like those in Figure 10.1 (taken from the data in Table 10.1); in this graph the numerical values of the factor levels dictate both their order and their spacing along the X axis. By contrast, for the data plotted in Figure 3.1, both the ordering and the spacing of the factor levels were arbitrary.