Background:
Measuring global progress in taxation (R) is an objective, tractable exercise but is challenging in comparison to progress on other measures of the WHO MPOWER package. Countries are grouped into four groups based on the share of total taxes in cigarette price: 0-25%, 25-50%, 50-75% and 75-100%). One challenge in this approach is that excise taxes are subsumed within total taxes. A second challenge is to explain whether progress in tax shares is driven by actual tax policy improvement.

Methods:
A ranking of countries by cigarette excise tax share was performed for each of the reports between 2008 and 2016 and this was compared with the published WHO rankings of total tax shares. Data on report-by-report changes in tax shares was used to compute transition probabilities for the published WHO R groupings to examine the likelihood of tax shares increasing or declining, both unconditionally and conditional to WHO regions and income-groupings.

Results:
Changes in country rankings of excise tax shares closely track changes in total tax shares ranking, providing credence to the use of the current tax share measure. Unlike the "POWE" groupings where retrogression in tobacco control progress is uncommon, countries´ tobacco tax shares are nearly as likely to fall as they are to rise. Between 2014 and 2016, total tax shares rose, was unchanged, and fell, in 96,24 and 75 countries respectively. When transition probabilities are examined, however, countries are significantly likely to stay within their tax grouping from year to year, with movement across groups driven by substantive tax policy changes.

Conclusions:
Total tax shares and groupings in the WHO GTCR largely capture excise tax policy differences over time. In 2016, 36 countries had total tax share between 65% and 75% in 2016, pointing to many countries being at the threshold of making the highest R category.