This graph plots Period 1 responses on the x-axis against Period 2 responses on the y-axis. Each sequence is represented by a different symbol. The diagonal line shows where the x-values and the y-values are equal, for example where x = 4 and y = 4.

Look for the following patterns:

·    Most points for one sequence appear above the line and most points for the other sequence appear below the line. This pattern indicates a treatment effect. The response to the test treatment is different than the response to the reference treatment.

·    Most points for one sequence appear in the lower left of the graph and most points for the other sequence appear in the upper right of the graph. This pattern indicates a sequence effect. The responses are generally higher for one sequence than the other.

·    Most points for both sequences appear on the same side of the line. This pattern indicates a period effect. The responses are generally higher during one period than the other.

·    The points for both sequences are scattered randomly on the graph. This pattern indicates that there is no effect of treatment, sequence, or period. The responses are generally the same regardless of these factors.

The period plot for the antacid data clearly shows a treatment effect. The following patterns indicate that, for both sequences, the brand-name antacid was more effective than the generic antacid at raising stomach pH:

·    For Sequence 1, almost all of the points are above the line. This indicates that stomach pH was higher during Period 2 than during Period 1. Period 2 is when the brand-name antacid was given for Sequence 1.

·    For Sequence 2, all of the points are below the line. This indicates that stomach pH was higher during Period 1 than during Period 2. Period 1 is when the brand-name antacid was given for Sequence 2.