Table 1.
General Characteristics of the Studies Included in the Final Analysis
| Study (reference) |
Country | Year enrolled | Follow-up time | Population (gender, age) | Number of cases | Outcome (ever use/ current use) | Definition of exposure | OR/RR (95% CI) | Adjusted variables | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 2016 Bold [17] | US | 2013 | 6 months | 340 ever e-cig users (12-17 years, 161 females and 179 males) | 170 | current use of e-cig | friends use e-cig (Yes vs No) | 1.36 (0.78-2.38) | school type, sex, race, traditional cigarette smoking status, other tobacco use | ||||||||
| 2018 Agarwal [18] | US | 2014 | 1 year | 2110 never e-cig users (18-29 years, 1401 females and 709 males) | 329 | ever use of e-cig | number of close friends using e-cig (scored on a scale from 0 [none] to 4 [all]) | 1.32 (1.11-1.57) | age, gender, race/ethnicity, school enrollment, number of other tobacco products used | ||||||||
| 2018 Urman [19] | US | 2014 | 1.5 years | 1164 never e-cig users (median age=17.3 years) | 326 | ever use of e-cig | number of friends using e-cig (1 or 2 vs 0) | 1.95 (1.26-3.02) | gender, ethnicity, parental education, community of residence, ever use of cigarettes, hookah or cigars | ||||||||
| (3 or 4 vs 0) | 4.08 (1.96-8.49) | gender, ethnicity, parental education, community of residence, ever use of cigarettes, hookah or cigars | |||||||||||||||
| 2018 East [20] | US | 2016 | 6 months | 1020 never e-cig users (11-18 years, 552 females and 468 males) | NA | ever use of e-cig | Some friend using e-cig (Yes vs No) | 3.03 (1.63-5.64) | Age, gender, school performance, problem behavior, monthly alcohol use, smoking susceptibility, e-cig susceptibility, some friends smoke, some friends use e-cigarettes, at least one parent smokes, at least one parent uses e-cigarettes, sibling(s) smoke, sibling(s) use e-cigarettes, public approve of smoking, and public approve of e-cigarettes | ||||||||
| 2019 Loukas (youth) [21] | US | 2014 | 2.5 years | 2288 never e-cig users and 359 cases (12-17 years, about 50% were females) | 359 | ever use of e-cig | A close peer using e-cig (scored on a scale from 1 [none] to 5 [all]) | 1.51 (1.14-1.99) | sex, race, ethnicity, current other tobacco use, sensation seeking, recall of exposure to e-cig marketing | ||||||||
| 2019 Loukas (young adults) [21] | US | 2014 | 2.5 years | 2423 never e-cig users and 611 cases (18-29 years, 67% were females) | 611 | ever use of JUUL e-cig | A close peer using e-cig (scored on a scale from 1 [none] to 5 [all]) | 1.37 (1.21-1.56) | sex, race, ethnicity, age, college type, current other tobacco use, sensation seeking, recall of exposure to e-cig marketing | ||||||||
| 2020 Vallone [22] | US | 2018 | 1 year | 6165 never e-cig users (15-34 years) | NA | ever use of JUUL e-cig current use of e-cig |
number of 4 closest friends using e-cig (scored on a scale from 0 [none] to 4 [all]) number of 4 closest friends using e-cig (scored on a scale from 0 [none] to 4 [all]) |
1.84 (1.59-2.12) 2.53 (2.05-3.11) |
age group, sex, race/ethnicity, perceived financial situation, region, sexual orientation age group, sex, race/ethnicity, perceived financial situation, region, sexual orientation |
||||||||
| 2021 Obinwa [23] | US (TATAMS) | 2014 | 3 years | 3733 participants (11-15 years) | NA | current use of e-cig | number of close friends using e-cig (a few – all vs. none) | 4.29 (2.89-6.38) | age, sex, and race/ ethnicity), socioeconomic class, academic performance, positive affect, sensation seeking, family member use of e-cig, social acceptability, social norm, recall of advertising for e-cig at stores, recall of social media tobacco promotion, and other substance use | ||||||||
| 2021 North [24] | US | 2018 | 1 year | 3543 participants (21-34 years, 66% were females) | 238 | current use of pod-vape | number of close friends using e-cig (scored on a scale from 0 [none] to 4 [all]) | 1.32 (1.11-1.58) | sex, age group, race/ethnicity, current e-cig use, current cigarette smoking, social norms, and risk perceptions | ||||||||
| 2022 Ahmad [25] | Canada | 2018 | 1 year | 668 participants (16-25 years, 251 females and 417 males) | 396 | current use of pod-type e-cig in the last 6 months | Proportion of friends using e-cig (many vs. none/some) | 2.15 (1.37-3.34) | age group, sex, province/territory, sensation seeking, vaping-related characteristics, polysubstance use, exposure to advertisements, and sensation seeking | ||||||||
| 2022 Wang [26] | US | 2016 | 1 year | 8560 never e-cig users (12-17 years) | 2393 | ever use of e-cig | number of best friends using e-cig (a few vs none) | 2.69 (2.27-3.18) | sex, age, race and ethnicity, highest parental education, severity of internalizing and externalizing mental health problems, perception of harm from e-cigarette use, current cigarette smoking status, and current use of other tobacco products | ||||||||
| number of best friends using e-cig (some vs none) | 3.69 (2.91-4.68) | ||||||||||||||||
| number of best friends using e-cig (most vs none) | 4.56 (3.14-6.63) | ||||||||||||||||
| number of best friends using e-cig (all vs none) | 4.08 (1.44-11.59) | ||||||||||||||||
| 1049 | current use of e-cig | number of best friends using e-cig (a few vs none) | 2.69 (2.27-3.18) | ||||||||||||||
| number of best friends using e-cig (some vs none) | 3.69 (2.91-4.68) | ||||||||||||||||
| number of best friends using e-cig (most vs none) | 4.56 (3.14-6.63) | ||||||||||||||||
| number of best friends using e-cig (all vs none) | 4.08 (1.44-11.59) | ||||||||||||||||