This line graph is to depict the line graphs that are frequently used in single system design studies (i.e. individual design studies). The graphic uses a smoking example with the number of cigarettes smoked on the Y axis and the days on the X axis. After 10 days, it shows that there was an intervention (the intervention could be something like the patch). The pretest phase is often labeled "A: Baseline" and the treatment phase is often labeled "B: Intervention."