Table 3. Multivariate logistic regression model (aOR^a, 95% CI) for the association between smoking status and psychological distress, and covariates among individuals aged 18–34, NHIS (n = 9,784).

	E-cigarette ever users onlyb vs. non-users	Former cigarette users & e-cigarette ever usersc vs. non-users	Current dual users (cigarette and e-cigarette)d vs. non-users	Current cigarette users onlye vs. non-users	Non-users (no cigarette or e-cigarette)f vs. any-users
Psychological distress (K6)g	aOR (95%CI)	aOR (95%CI)	aOR (95%CI)	aOR (95%CI)	aOR (95%CI)
0	Referent	Referent	Referent	Referent	Referent
1–2	1.4 (1.0, 2.1)	2.2 (1.5, 3.4)**	1.5 (0.9, 2.5)	0.9 (0.7, 1.3)	0.8 (0.6, 0.9)*
3–5	2.3 (1.6, 3.4)**	3.0 (1.9, 4.9)**	1.7 (1.0, 2.9)	1.3 (0.9, 1.8)	0.5 (0.4, 0.6)**
6–10	2.1 (1.3, 3.2)*	3.2 (1.9, 5.4)**	2.5 (1.5, 4.2)**	1.9 (1.1, 3.4)*	0.5 (0.4, 0.6)**
11–24	3.5 (1.2, 9.7)*	3.2 (1.7, 6.1)**	5.0 (2.8, 8.9)**	2.5 (1.6, 3.8)**	0.3 (0.2, 0.4)**

^aAdjusted for gender, race/ethnicity, poverty ratio, educational level, employment status, marital status, region and health insurance

^bE-cigarette ever users only were defined as individuals who answered “yes” to the question about ever using an e-cigarette and “no” to the question “Have you smoked at least 100 cigarettes in your entire life?”

^cFormer cigarette users & e-cigarette ever users were defined as those who responded “yes” to the question about ever using an e-cigarette and had smoked at least 100 cigarettes in their lifetime but who had quit smoking at the time of interview.

^dCurrent dual users included current cigarette users and those who answered “yes” to the question about ever using an e-cigarette and answered “every day” or “on some days” to the question “Do you now use e-cigarettes every day, some days, or not at all?”

^eCurrent cigarette users only were defined as those who had smoked 100 cigarettes in their lifetime, smoked “every day” or “on some days” at the time of the survey, and responded “no” to the question about ever using an e-cigarette.

^fNon-users were defined as those who had never used either e-cigarettes or cigarettes.

^gK6 scores were grouped into five levels of distress (0, 1 to 2, 3 to 5, 6 to 10, and ≥11)

CI = confidence intervals; NH = non-Hispanic; K6 = Kessler 6;aOR = adjusted odds ratio; FPL = federal poverty line

*p<0.05

**p<0.001