Product types and outcome measures of included studies
| Sample characteristics | N | US* studies (n=23) | Non-US† studies (n=17) |
|---|---|---|---|
| Product type | |||
| E-cigarette | 17 | 10 | 7 |
| Cigarette | 10 | 4 | 6 |
| Little cigar, cigarillo, cigar | 4 | 2 | 2 |
| Hookah | 3 | 2 | 1 |
| Various tobacco products | 3 | 2 | 1 |
| Smokeless tobacco | 2 | 2 | 0 |
| Bidi | 1 | 1 | 0 |
| Outcome measures‡ | |||
| Taste, appeal, risk perceptions | 11 | 4 | 7 |
| Preference | 10 | 4 | 6 |
| Expectancies and beliefs | 6 | 3 | 3 |
| Reasons for use | 7 | 5 | 2 |
| Intention to try, initiation | 12 | 7 | 5 |
| Progression to regular use | 2 | 1 | 1 |
| Dual/poly use | 3 | 2 | 1 |
| Quit intention and quitting behaviour | 4 | 2 | 2 |
*One study included participants (13%) outside the USA.20
†One study included participants (41%) from the USA.21
‡Categories are not mutually exclusive.