***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: BACKGROUND Few national surveys document the prevalence of e-cigarette use in the U.S. The existing metric to assess current use likely identifies individuals who have recently tried an  e-cigarette  but do not continue to use the product . PURPOSE To document the prevalence of e-cigarette ever use , current use , and established use in a nationally representative survey of current and former cigarette smokers in the U.S. METHODS A r and om sample of current and former cigarette smokers completed a web-based survey in June 2013 ( n=2,136 ) . Data were analyzed in November 2013 . Multivariate logistic regression identified demographic and smoking-related factors associated with each use category . Point estimates with 95 % CIs described e-cigarette use behaviors ( e.g. , preferred br and , purchasing patterns ) for each group . RESULTS Almost half of respondents had tried e-cigarettes ( 46.8 % ) , but prevalence of established use remained low ( 3.8 % ) . Although trial of e-cigarettes was highest among daily smokers , the odds of being an established e-cigarette user were greater for former smokers ( OR=3.24 , 95 % CI=1.13 , 9.30 , p<0.05 ) . Furthermore , e-cigarette preference and use patterns varied among ever , current , and established users . Established users reported using rechargeable e-cigarettes  , having a regular br and , and using e-cigarettes at home and in the workplace at much higher levels than the " current use " metric captures . CONCLUSIONS Improved survey measures for e-cigarette use are needed . The identification of established e-cigarette users may provide insight to product features or other individual factors that are associated with sustained use of e-cigarettes BACKGROUND Electronic cigarettes , or e-cigarettes , are battery operated devices that deliver nicotine via inhaled vapor . There is considerable controversy about the disease risk and toxicity of e-cigarettes and empirical evidence on short- and long-term health effects is minimal . Limited data on e-cigarette use and correlates exist , and to our knowledge , no prevalence rates among U.S. college students have been reported . This study aim ed to estimate the prevalence of e-cigarette use and identify correlates of use among a large , multi-institution , r and om sample of college students . METHODS 4444 students from 8 colleges in North Carolina completed a Web-based survey in fall 2009 . RESULTS Ever use of e-cigarettes  was reported by 4.9 % of students , with 1.5 % reporting past month use . Correlates of ever use included male gender , Hispanic or " Other race " ( compared to non-Hispanic Whites ) , Greek affiliation , conventional cigarette smoking and e-cigarette harm perceptions . Although e-cigarette use was more common among conventional cigarette smokers , 12 % of ever e-cigarette users had never smoked a conventional cigarette . Among current cigarette smokers , e-cigarette use was negatively associated with lack of knowledge about e-cigarette harm , but was not associated with intentions to quit . CONCLUSIONS Although e-cigarette use was more common among conventional cigarette smokers , it was not exclusive to them . E-cigarette use was not associated with intentions to quit smoking among a sub- sample of conventional cigarette smokers . Unlike older , more established cigarette smokers , e-cigarette use by college students does not appear to be motivated by the desire to quit cigarette smoking Although electronic cigarettes ( e-cigarettes ) are aggressively promoted as smoking cessation aids,1 studies of their effectiveness for cessation have been unconvincing.2 , 3 One r and omized trial comparing e-cigarettes with and without nicotine , and nicotine patch found no differences in 6-month quit rates.2 Population -based , longitudinal studies have also not shown associations between e-cigarette use and quitting.4 , 5 A longitudinal , international study found that , although 85 % of smokers who used e-cigarettes reported using them to quit , e-cigarette users did not quit more frequently than non-users (p=.516).4 Among US quitline callers , e-cigarette users were less likely to have quit at 7 months than non-users.5 We employed a longitudinal analysis of a national sample of current US smokers to determine whether e-cigarette use predicted successful quitting , or reduced cigarette consumption PURPOSE Electronic cigarettes ( e-cigarettes ) are a new type of device that delivers vaporized nicotine without the tobacco combustion of regular cigarettes . We sought to underst and awareness of and willingness to try e-cigarettes among adolescent males , a group that is at risk for smoking initiation and may use e-cigarettes as a " gateway " to smoking . METHODS A national sample of 11 - 19-year-old males ( n = 228 ) completed an online survey in November 2011 . We recruited participants through their parents , who were members of a panel of U.S. households constructed using r and om-digit dialing and addressed-based sampling . RESULTS Only two participants ( < 1 % ) had previously tried e-cigarettes . Among those who had not tried e-cigarettes , most ( 67 % ) had heard of them . Awareness was higher among older and non-Hispanic adolescents . Nearly 1 in 5 ( 18 % ) participants were willing to try either a plain or flavored e-cigarette , but willingness to try plain versus flavored varieties did not differ . Smokers were more willing to try any e-cigarette than nonsmokers ( 74 % vs. 13 % ; OR 10.25 , 95 % CI 2.88 , 36.46 ) . Nonsmokers who had more negative beliefs about the typical smoker were less willing to try e-cigarettes ( OR .58 , 95 % CI .43 , .79 ) . CONCLUSIONS Most adolescent males were aware of  e-cigarettes  , and a substantial minority were willing to try them . Given that even experimentation with e-cigarettes could lead to nicotine dependence and subsequent use of other tobacco products , regulatory and behavioral interventions are needed to prevent " gateway " use by adolescent nonsmokers . Campaigns promoting negative images of smokers or FDA bans on sales to youth may help deter use AIM To investigate New Zeal and ers ' use , perceptions and views on the acceptability of electronic cigarettes ( e-cigarettes ) .  METHOD 840 current smokers and recent quitters were recruited through r and om digit dialling as part of the New Zeal and Smoking Monitor ( NZSM ) , a 33-item telephone-based survey delivering 120 interviews per fortnight . Two sets of questions were deployed at different times to assess ever-purchase of e-cigarettes  , perceptions of the safety and cessation efficacy of e-cigarettes , and acceptability of using them instead of tobacco cigarettes or as a cessation aid . RESULTS 7 % of the sample reported having purchased an e-cigarette . One-third of respondents believed them to be safer to use than tobacco cigarettes , and could help people quit smoking tobacco . Forty-one percent considered it acceptable to use  e-cigarettes  as a replacement product and 58 % as a cessation aid . Responses differed according to ethnicity , age and household income . CONCLUSION Purchasing ( and therefore we assume , use ) of e-cigarettes in New Zeal and is uncommon . Despite this finding , many respondents viewed e-cigarettes in a positive light and indicated willingness to use them . Ongoing monitoring on the use of and public attitudes towards this emerging product is recommended 
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Data synthesis Results of narrative synthesis suggest broadly that awareness , ‘ ever use ’ and current use of e-cigarettes may be particularly prevalent among older adolescents and younger adults , males , people of white ethnicity and —particularly in the case of awareness and ‘ ever use’—those of intermediate or high levels of education .
Conclusions E-cigarette awareness , ‘ ever use ’ and current use appear to be patterned by a number of sociodemographic factors which vary between different countries and subnational localities .