Until now, we’ve been looking at only one phase. Most of the time, we implement an intervention because we want to increase or decrease the level of the behavior. If we are trying to decide whether an intervention caused a change in behavior, we need to compare the behavior in the baseline phase to the behavior in the treatment phase. To make this comparison, we first look at the level of the data path in the baseline phase and then look at the level of the data path in the treatment phase. If the level is different, then the treatment might have caused that change.