Analysing the Spanish smoke-free legislation of 2006: a new method to quantify its impact using a dynamic model.

BACKGROUND: There are many models that study aspects of smoking habits: the influence of price, tax, relapse time, and the effects of prohibition. There are also studies examining the effects of the Spanish smoke-free law. We wanted to build a model able to separate the effect of the law from the pre-law evolution of smoking habits.
METHODS: Using data from the Spanish Ministry of Health and Social Policy, we developed a dynamic model of tobacco use. The model projects the evolution over time of the number of non-smokers, smokers and ex-smokers before 2006. Then, we compared the predictions of the model with data for the years after the law came into force, 2006 and 2009.
RESULTS: We show that smoke-free law has had a significant impact on different sub-populations. The number of ex-smokers increased significantly in 2006 and this increase was maintained in 2009. The number of smokers also decreased significantly in 2006, but in 2009 this returned to its value before the law. Simultaneously, the number of non-smokers decreased in 2009.
CONCLUSIONS: When the law came into force (2006), its restriction on smoking in public and work places made many smokers decide to give up smoking, decreasing the number of smokers and increasing the number of ex-smokers. In 2009, the majority of those who succeeded in giving up smoking did not return to the habit. However, the smoke-free law had no effect on new smokers and the number of smokers returned to previous levels, whereas the number of non-smokers decreased. Therefore, we can conclude that the law had a very positive effect in the first few years but this has dissipated over time, with the exception of ex-smokers, whose number is still higher than before the law.