In Figure 14.7(a) the data provide evidence for a cause-and-effect relation- ship by showing a change in level each time the treatment is introduced or withdrawn. It is also possible to demonstrate a cause-and-effect relationship by showing a change in trend.
In Figure 14.7(b), for example, the decreasing trend is stopped when the treatment is introduced. Behavior returns to the baseline trend when the treatment is withdrawn, and the stable level returns when the treatment is reintroduced.