Summary of main characteristics of the 20 included papers
| Characteristic | Categories | Number (%)* | References |
| Study design† | Experimental and quasiexperimental studies | 9 (45%) | 26 27 29 32 36 39 40 42 44 |
| Cohort studies | 2 (10%) | 25 41 | |
| Cross-sectional studies | 4 (20%) | 30 31 34 43 | |
| Not specified | 5 (25%) | 28 33 35 37 38 | |
| Country | Canada | 1 (5%) | 27 |
| Wales | 1 (5%) | 43 | |
| South Korea | 1 (5%) | 31 | |
| USA | 17 (85%) | 25 26 28–30 32–42 44 | |
| Intervention type | Non-policy | 13 (65%) | 26–29 32 35–37 39–42 44 |
| Policy | 7 (35%) | 25 30 31 33 34 38 43 | |
| Primary outcomes‡ | Ever use of vaping products§ | 6 (30%) | 25 30 33 38 39 43 |
| Initiation of vaping | 3 (15%) | 25 27 41 | |
| Susceptibility to vaping | 8 (40%) | 26 28 29 32 34 39 40 42 | |
| Beliefs and perceptions on harms, risks and social norms | 7 (35%) | 26 28 34 36 40 42 44 | |
| Attitudes and behaviours | 4 (20%) | 28 34 36 42 | |
| Knowledge | 2 (10%) | 26 37 | |
| Reactions to the interventions | 1 (5%) | 29 | |
| Perceptions of the effectiveness of the interventions | 4 (20%) | 28 31 35 36 | |
| Level of intrusiveness of the interventions¶** | Eliminate choice | 5 (25%) | 25 30 34 38 43 |
| Restrict choice | 1 (5%) | 43 | |
| Guide choices through disincentives | 1 (5%) | 38 | |
| Guide choices through incentives | – | – | |
| Guide choices by changing default policy | 4 (20%) | 29 31 33 43 | |
| Enable choice | 2 (10%) | 39 40 | |
| Provide information | 9 (45%) | 26–28 32 35–37 42 44 | |
| Do nothing or simply monitor the current situation | 1 (5%) | 41 | |
| Reorient government action | 1 (5%) | 43 | |
| Quality appraisal†† | Strong | 4 (20%) | 25–28 |
| Moderate | 5 (25%) | 29–33 | |
| Weak | 11 (55%) | 34–44 |
*All percentages calculated with 20 articles in the denominator.
†Study design as informed by authors.
‡Some papers included multiple outcomes.
§Past-month e-cigarette use was used as a proxy of ever e-cigarette use.
¶The level of intrusiveness of interventions was based on the PLACE Research Lab Intervention Ladder Policy Analysis Framework21 (modified version of the Nuffield Council on Bioethics intervention Ladder22).
**Some papers reported on multiple interventions, and therefore, they were assigned different levels of intrusiveness.
††The Effective Public Health Practice Project Quality Assessment Tool for Quantitative Studies24 was used to assess methodological quality of the included studies.