Akl et al. BMC Public Health 2011, 11:244 http://www.biomedcentral.com/1471-2458/11/244 Page 2 of 12 Coal Body Bowl (water) Tobacco Head Hose Mouth piece Akl et al. Figure 1 Annotated figure of a waterpipe smoking device. Recent studies have reported relatively high prevalence rates of waterpipe tobacco smoking in Middle Eastern countries, [10] but also in western countries such as the United States, [2,11] the United Kingdom, [12] and Aus- tralia [13]. In 2005, the World Health Organization (WHO) issued an advisory note calling for a better understanding of national and global trends of waterpipe tobacco smoking [14]. In 2007, the American Lung Association labeled waterpipe smoking as an ‘emerging deadly trend’ [2]. The association called for more research on the patterns of use of waterpipe amongst various populations and to investigate its use as part of the national surveys on youth and adult tobacco use. The primary objective of our study was to systematically review the medical literature for the prevalence of water- pipe tobacco use among the general population as well as specific populations. A secondary objective was to identify the factors associated with waterpipe tobacco use. Methods No protocol for this review has been published. Eligibility criteria Inclusion criteria were: Cohort studies and cross sectional studies Assessment of the prevalence of use of waterpipe for the purpose of tobacco smoking. The target population is either the general popula- tion or a specific population of interest such as high school students, university students, and pregnant women. Prevalence of waterpipe smoking reported sepa- rately from the prevalence of other forms of smoking Exclusion criteria were: Convenience sampling Sampling methodology did not clearly lead to a representative sample of the target population (e.g., excluding cigarette smokers). No measure of prevalence Search Strategy We electronically searched the following databases in June 2008, MEDLINE (1950 onwards), EMBASE (1980 onwards), and ISI the Web of Science using no language restrictions. The search strategy was based on related systematic review, [15] a review of eligible papers, and an Internet search for the synonyms of waterpipe (Addi- tional file 1) [15]. We also used the ‘Related Articles’ feature in PubMed and reviewed the reference lists of included and relevant papers. Selection process Two reviewers independently screened the title and abstract of identified citations for potential eligibility. They then used a standardized and pilot-tested form to independently screen the full texts of citations judged potentially eligible by at least one reviewer. They resolved disagreements by discussion or using an arbitrator. Data abstraction Two reviewers used a standardized and pilot-tested form to independently abstract data and resolved disagree- ments by discussion or using an arbitrator. Abstracted data related to the following: Study methodology: sampling frame, sampling method, recruitment method, and administration method Methodological quality: sample size calculation, validity of tool, pilot testing, and response rate Population: country, target population, setting (location and time period), and numbers sampled, participated, and analyzed