Estimating the population health impact of recently introduced modified risk tobacco products: a comparison of different approaches.

We review approaches used to estimate the population health impact of introducing a Modified Risk Tobacco Product (MRTP). Thirteen models are described, some focussing on e-cigarettes, others more general. Most models are cohort-based, comparing results with or without MRTP introduction. They typically start with a population with known smoking habits and then use transition probabilities either to update smoking habits in the "null scenario" or to update joint smoking and MRTP habits in the "alternative scenario". The models vary in the tobacco groups and transition probabilities considered. Based on aspects of the tobacco history developed, the models compare mortality risks, and sometimes life-years lost and health costs, between the scenarios. Estimating the effects on population health depends on frequency of use of the MRTP and smoking, and on the extent to which the products expose users to harmful constituents. Strengths and weaknesses of the approaches are summarized. Despite methodological differences, most modellers have assumed that the increase in risk of mortality from MRTP use, relative to that from cigarette smoking, is very low and have concluded that MRTP introduction is likely to have a beneficial impact. Further model development, supplemented by preliminary results from well-designed epidemiological studies, should enable more precise prediction of the anticipated effects of MRTP introduction.