Population health and the hardcore smoker: Geoffrey Rose revisited.

The "hardening hypothesis" suggests that as smoking prevalence decreases, lighter smokers will quit first, leaving more "hardcore" smokers in the population. At a population level, however, the weight of evidence suggests that no hardening is occurring. By understanding the lessons from Geoffrey Rose's model of population-level risk factor change, we argue that the hardening of the smoking population is not inevitable. The Rose model predicts that the effect of policy interventions, and changes in social norms, can shift the population-level risk distribution for continuing to be a smoker, making it more likely that all smokers will quit. This analysis also suggests that further reductions in smoking prevalence will not come without further changes in the underlying--and largely cultural--root causes of smoking in a population.