 equaled or exceeded 20% of their annual expenditure per adult equivalent.

Cigarette tax revenues and household expenditure on cigarettes
We calculated post-policy tax revenues generated from raising the cigarette excise tax. The magnitude of annual change is the product of the change in the number of packs of cigarettes consumed per smoker per year, the number of smokers in a given quintile, and the change in excise tax per cigarette pack. Likewise, changes in the amount of household expenditure devoted to cigarettes following increased price were estimated. (More details are given in Appendix 6 & 7 in the supplementary document).

Sensitivity analysis
To assess the robustness of our findings, we undertook several univariate sensitivity analyses. First, we simulated impact under the scenarios of varying increases in the retail price of a pack of cigarettes (25%-and 100%-point increases). Second, we tested the effect of brand switching by considering a parameter that shows the percentage of smokers who, in response to rising cigarette prices instead of quitting or reducing their consumption, tend to low-priced brands (ie, "switchers", was set at either 0, 33%, or 75%) on the number of premature smoking-related deaths avoided, changes in tax revenues from cigarettes, years of life gained, and the amount of out-of-pocket expenditures averted by quintiles (Fig. 1). Third, we modeled financial risk protection using two alternative poverty thresholds: a lower poverty line of US$ 1.9, and an upper poverty line of US$ 5.5 per day per

Results
Estimates of participation price elasticities of demand for cigarettes ranged from -0.07 to − 0.12, and conditional price elasticities from − 0.32 to − 0.40 (Tables 2, and 3 in the supplementary appendix provide more information on regression results). The estimates seem to be consistent with the result of a prior study with an estimate of − 0.45 [35]. The increasing body of research in low and middle-income countries indicates that price affects both participation (prevalence) and consumption, although the magnitude of these effects varies greatly across studies. For example, Jime'nez-Ruiz et al. in Mexico (2007) found that the price elasticity of smoking participation and consumption is − 0.06 and − 0.45, respectively [36]. In contrast, Lance and colleagues (2004) estimated a total price elasticity of − 0.127 with a conditional price elasticity of − 0.026 and participation price elasticity of − 0.101 in Russia [37]. These differences can be accounted for in part by research design and sample sizes. This study found that a75% price increase in cigarettes would reduce current consumption in all 5 quintiles, pushing 501,735 current male smokers to quit or not to start. This is roughly equivalent to 8% of the total current male cigarette smokers in Iran in 2020. A 75% cigarette price increase in Iran and consequent fall in demand for it would save 198,507 lives and about 1.9 million years of life projected over 60 years, of which 11% would be gained by the lowest expenditure quintile. This distribution is determined by the lower participation price elasticity of − 0.07% for poorer smokers, indicating they are more inelastic with respect to change in cigarette prices, and thus quitting in fewer numbers.
Since the outcomes of interest except for tax revenues occur over long-time horizons in our analysis (60 years), discounting is required to obtain the present value of the stream of two key outcomes including the number of cigarette quitters and years of life gained as a result of the policy implementation. These two key results were presented for a 3% discount rate to illuminate the effect of discounting. When discounting, this policy would avert 134,239 smoking-related premature deaths and would save about 1.1 million years of life. The analysis shows a 75% cigarette tax increase in the following year (end of the first year) would save 6106 lives and 48,727 years of life. Therefore, the average years of life gained per smoker having quitted cigarette smoking is about 4 years or 5.3% of the life expectancy of men in Iran. If "health" is defined by average life expectancy, the health production elasticity of taxing cigarettes on the margin can be estimated using the following equation; By simple extrapolation, a 1% increase in cigarette tax in Iran (about 1 cent per pack) would mean an increased average life expectancy of 0.07 years for quitters.
We estimated that 85,913 heart disease-related deaths, 8054 lung cancer-related deaths, 10,739 COPD-related deaths, and 29,533 stroke-related deaths could be averted.
A societal perspective was adopted for the analysis and consequences for household private expenditures and health systems were evaluated. From the patient's viewpoint, we assessed the amount of averted out-of-pocket costs resulting from taxing cigarettes. Depending on the provider's perspective, the total averted costs of the The distribution of outcomes by percentage per expenditure quintile is represented in parentheses tobacco-related diseases to the government and social health insurance were estimated. Under the 75% tax, we projected a reduction of US$196.4 million in health expenditures. Consequently, averted out-of-pocket expenditures due to smoking cessation that leads in turn to the lower incidence of smoking-related diseases would aggregate to US$ 80.5 million. Assuming that there is no difference in the distribution of out-of-pocket payments among quintiles, around 22% of the overall out-ofpocket expenditures averted were concentrated in the highest quintile, while the lowest quintile could save 9% of them. Scaled to the total number of male smokers, these figures represent $31 of health care cost savings per smoker, or roughly $13 of OOP savings per smoker. Based on our estimate, raising the cigarette tax by 75% of retail prices in Iran would generate a total of about US$ 1 billion in excise revenue for 2017, 29% of which would be borne by the bottom two quintiles, compared with 46% in the top two quintiles. In terms of change in expenditures on cigarettes under the same tax increase, we estimated that the lowest quintile would experience 1.95% (US$ 38 million) increases in expenditures while the two highest quintiles would see increases in expenditures on the cigarette of 0.85% (about US$ 57 million) and 0.89% (US$ 78 million) of their budget, respectively. We consider that gamma distribution appreciably fits the data of expenditure as a proxy for income [38], under the fitted model 11% of the Iranian population is already below the poverty line with respect to poverty headcount ratio at $3.20 a day as defined by the World Bank. The number of averted cases of impoverishment was calculated as individuals whose annual income would have decreased to less than US$ 3.20 per day after paying out of pocket for smoking-related disease treatment. In terms of financial risk protection, we estimated that 17,244 new poverty cases and 56,287 cases of catastrophic health expenditures would be averted following a reduction in health expenses resulting from the implementation of the tax policy.

Discussion
This is the first study in Iran conducted by employing a method of ECEA to quantify the effect of a 75% price increase in cigarettes as proposed by WHO on health benefits, health expenditures, additional tax revenues, changes in household expenditures on the cigarette, and financial risk protection. Depending on the values of included parameters, the results of this study indicate that the policy could avert 198,507 premature deaths from the four major smoking-related diseases and could save about 1.9 million years of life (11% of these in the poorest group) over a 60-year time horizon. and generate cigarette excise revenue amounting to about $US1billion (0.23% of GDP in 2017) in the male population.
Increasing tobacco-product taxes will generate sustainable revenues over the short to medium term. In the long run, persistent increases in tobacco tax along with other tobacco control efforts will lead to a higher drop in tobacco consumption and, to a reduction in tobacco taxes revenues. Nevertheless, it is worth noting that decreased tobacco tax revenues would have been replaced by improving public health and averting the costs of the harmful effects of smoking [39].
A rather increasing gradient from the bottom to the top quintiles in the number of life-years gained and in the amount of averted health expenditure on smokingrelated diseases might be accounted for the lower prevalence of cigarette smoking, lower participation elasticity, and lower absolute number of smokers among the poorer quintiles. In this study, the impact of the tax policy was found to offer financial protection for households by preventing the risk of impoverishment and catastrophic health expenditure resulted from tobaccorelated diseases. The study found that financial risk protection benefits wholly concentrated in the bottom quintiles.
Although the benefits of taxing cigarettes concerning reductions in health care costs and, in turn, the amount of out-of-pocket expenditure, as well as health benefits including premature deaths averted and life-years gained are mainly concentrated among the top 60% of the population, the benefits of financial risk protection would accrue to the bottom two expenditure quintiles. A comprehensive account of impacts does not demonstrate that cigarette taxation to be regressive, especially if the price elasticity of demand for tobacco products and price increases would be large [40]. As Table 2 shows, cigarette taxation would have a greater impact on richer groups. Although these results differ from some published studies [12,15,41], as to which strata of society benefit, they are consistent with findings of a study that has examined the effect of the tobacco tax in the Kyrgyz Republic [42]. The study has confirmed the findings of a similar previous study in Turkey in 2010 which found cigarette price increase would reduce the number of smokers by 590,000 and would save an estimated 340,000 lives [43].