Figure 1.

Block diagram depicting the relation between Current Craving and CPD as a self-regulatory process. Current Craving is the variable representing the average craving level for each day in the time period examined. CPD is the variable representing the total number of cigarettes smoked each day in the time period examined. Baseline Craving Level is a constant value equal to the average prequit daily craving level. For each day, Daily Craving Difference equals the difference between Baseline Craving Level and the value of Current Craving for that day. Quit is the variable representing the attempt to quit smoking (Quit = 0 prior to the target quit day and Quit = 1 beginning on the target quit day).