The power of the study can be calculated specifically for each of these statistical techniques, most simply by the two-sample proportion test for PP and PA. This study (n=900 in both arms) is adequately powered (Type II error 0.80, type I error 0.05) to detect a true difference (in PP or PA) of 5% between the two arms, within the range of 10% vs. 20% quit rate in the two arms. Within this (10-20%) range, the study power is sensitive to any decrease in this difference, but allows less difference (7.5%) if the quit rate falls between 5% and 15% in the arms.