Martin et al. (1996) propose that stage movement is a better
outcome to assess the effectiveness of smoking cessation interventions
because, among other reasons, it is more common than
stopping smoking and trials would have more power to detect an
effect. In this study, there were very small and not statistically
significant advantages for the TTM arm in the quitting outcomes
(Aveyard et al., 2003), and it was plausible that the benefit was
obscured because quitting was rare and the analysis lacked power.