We identified self-reported current tobacco use in the included studies. Our preferred term was “daily tobacco use”, which we defined as either cigarettes smoked per day or by use of the term “regular smoking”, or a Fagerström Test for Nicotine Dependence score. If the study used
terms such as “current smoker” or “smoker” without stipulating the number of cigarettes or packs smoked per day, we did not judge tobacco use to be daily and we did not include the study in the analysis of daily smokers.