Table 2 Classification of 20,836 US adult frequent e-cigarette users into six Tobacco Use Pathway Groups (TUPs)
| Num. | TUP group | N | % of total sample | % of frequent EC users |
|---|---|---|---|---|
| 1 | Switchers | 15,807 | 70.5 | 75.9 |
| 2 | Dual users of cigarettes and e-cigarettes | 1330 | 5.9 | 6.4 |
| 3 | Former smoker-turned-dual users | 129 | 0.6 | 0.6 |
| 4 | Former-smoker e-cigarette users | 2483 | 11.1 | 11.9 |
| 5 | Never-smoker-turned-dual users | 31 | 0.1 | 0.1 |
| 6 | Never-smoker e-cigarette users | 1056 | 4.7 | 5.1 |