If the independent variable had no effect in this experiment, the subjects in all the groups should have evaluated the mugs about equally. We would not expect to see any dramatic difference from one group to another; the only differences we would see would be those caused by error. If that were the case, the means of the individual treatment groups would all be about the same. We could compute one overall mean, or grand mean, an average of all the treatment means. If our independent variable had no effect, the grand mean would describe the data about as well as three separate means, one for each of the three separate groups. But imagine what would happen if the independent variable really did have an effect on the value of the mugs. We could still compute an overall grand mean that would represent an average for all the groups: however, the means of the individual groups would be quite different from the grand mean. They would also be quite different from one another.