Patterns of simultaneous and concurrent alcohol and marijuana use among adolescents

Figures & data

Table 1. Model fit indices for 1 to 5 latent classes.

Classes	Parameters Estimated	AIC	BIC	a-BIC	VLMR	Entropy	Loglikelihood
1	5	382609.0	382655.8	382639.9	—	—	−191299.5
2	11	310841.0	310943.8	310908.8	0.333	0.949	−155409.5
3	17	308159.1	308318.0	308263.9	0.000	0.873	−154062.5
4	23	307566.2	307781.2	307708.1	0.000	0.838	−153760.1
5	29	307578.1	307849.2	307757.0	0.502	0.856	−153760.1

Notes: Bold font indicates class solution selected. Models were also run for 6 and 7 classes; however, there was no change in loglikelihood, and AIC, BIC and a-BIC were increasing, indicating the model fit was not improved by expanding the number of latent classes.

Table 2. Class membership for the 4-class model.

		Latent Classes
		SAM^a-Heavier Use	SAM-Lighter Use	Concurrent Use	Alcohol-Only Use
Estimated Membership Probabilities		0.112	0.216	0.107	0.564
	Item response probabilities
	Overall
SAM use
No 12-month SAM use	.682	0.017	0.040	1.000	1.000
Any past 12-month SAM use	.318	0.983	0.960	0.000	0.000
Alcohol use
No past 12-month alcohol or 2-week binge drinking	.011	0.001	0.000	0.096	0.000
Any past 12-month alcohol use, no binge drinking	.637	0.098	0.527	0.656	0.789
Any past 2-week binge drinking	.352	0.900	0.473	0.248	0.211
Marijuana use
No past 12-month or 30-day marijuana use	.538	0.000	0.000	0.000	0.951
Any past 12-month marijuana use, no 30-day use	.163	0.000	0.402	0.497	0.042
Any past 30-day marijuana use	.298	1.000	0.598	0.503	0.007

Notes: Unweighted N = 84,805. Bold font indicates item response probabilities ≥ .50.

^aSAM = simultaneous alcohol and marijuana use.

Figure 1. Four-class solution for latent class analysis of simultaneous and concurrent alcohol and marijuana use among U.S. 12th grade students, 1976–2016.

Table 3. Covariate descriptives.

Covariate	%	(SE%)
Gender
Female	48.4%	(0.3)
Male	46.0%	(0.3)
Missing	5.6%
Race/Ethnicity
White	70.9%	(0.6)
Black/African American	9.2%	(0.4)
Hispanic	7.7%	(0.3)
Other Races	7.0%	(0.2)
Missing	5.1%
Parent Education
High school or less	33.0%	(0.4)
Some college or more	59.3%	(0.4)
Missing	7.7%
High school grades
Grades of B- or better	70.0%	(0.3)
Grades of C+ or lower	21.8%	(0.3)
Missing	8.2%
Four-year college graduation plans
No definite plans to graduate	45.7%	(0.4)
Definitely plan to graduate	43.4%	(0.4)
Missing	10.9%
Evenings out for fun/recreation
Less than 3 evenings out/week	44.9%	(0.2)
Three or more evenings out/week	45.0%	(0.2)
Missing	10.1%
Truancy
No classes cut in the past month	57.6%	(0.3)
Any classes cut in the past month	31.0%	(0.3)
Missing	11.4%
Illicit drug use other than marijuana (IOTM)
No past 12-month IOTM use	67.0%	(0.3)
Any past 12-month IOTM use	23.5%	(0.3)
Missing	9.5%
Cohort^a
1976–1985	33.0%	(1.1)
1986–1995	26.5%	(1.0)
1996–2005	20.6%	(0.8)
2006–2016	19.9%	(0.8)

Notes: Unweighted N = 84,805; estimates provided account for the complex sample design.

SE% = standard error of the percentage (SE not reported for missing dummy terms).

^aNo missing data for this covariate.

Table 4. Adjusted relative risk ratios from multivariable multinomial logistic regressions of latent class membership on covariates: Comparisons with the SAM^a-Heavier Use class.

	SAM-Lighter Use		Concurrent Use		Alcohol-Only Use
	(vs. SAM-Heavier)		(vs. SAM-Heavier)		(vs. SAM-Heavier)
	ARR^b	p	ARR	p	ARR	p
Gender (ref = female)
Male	0.28	<.001	0.29	<.001	0.27	<.001
Race/Ethnicity (ref = White)
Black/African American	3.50	<.001	6.11	<.001	3.64	<.001
Hispanic	1.29	0.067	1.79	<.001	1.62	<.001
Other Races	1.43	0.005	1.86	<.001	1.73	<.001
Parent Education (ref = high school or less)
Some college	0.96	0.523	0.87	0.028	0.81	<.001
High school grades (ref = B- or better)
C+ or worse	0.87	0.030	0.94	0.331	0.62	<.001
Four-year college graduation plans (ref = no definite plans to graduate)
Definitely plan to graduate	1.22	0.004	1.15	0.038	1.33	<.001
Evenings out (ref = fewer than 3)
Three or more evenings out/week	0.37	<.001	0.33	<.001	0.25	<.001
Truancy (ref = no cutting class in past month)
Any classes cut in past month	0.50	<.001	0.43	<.001	0.26	<.001
Illicit drug use other than marijuana (IOTM) (ref = no past 12-month use)
Any past 12-month IOTM use	0.16	<.001	0.09	<.001	0.02	<.001
Cohort (ref = 2006–2016)
1976–1985	0.39	<.001	0.33	<.001	0.43	<.001
1986–1995	0.67	<.001	0.46	<.001	1.12	0.293
1996–2005	0.58	<.001	0.52	<.001	0.69	0.001

Notes: Unweighted N = 84,805. All covariates were entered simultaneously and included missing data indicators; estimates for missing indicators not shown. Bold entries represent associations significant at p < .01.

^aSAM = simultaneous alcohol and marijuana use.

^bARR = Adjusted risk ratio.

Table 5. Adjusted relative risk ratios from multivariable multinomial logistic regressions of latent class membership on covariates: Comparisons with the Alcohol-Only Use class.

	SAM^a-Lighter Use		Concurrent Use
	(vs. Alcohol Only)		(vs. Alcohol Only)
	ARR^b	p	ARR	p
Gender (ref = female)
Male	1.06	0.045	1.06	0.081
Race/Ethnicity (ref = White)
Black/African American	0.96	0.440	1.68	<.001
Hispanic	0.80	<.001	1.10	0.118
Other Races	0.83	<.001	1.07	0.264
Parent Education (ref = high school or less)
Some college	1.18	<.001	1.08	0.041
High school grades (ref = B- or better)
C+ or worse	1.39	<.001	1.51	<.001
Four-year college graduation plans (ref = no definite plans to graduate)
Definitely plan to graduate	0.92	0.003	0.86	<.001
Evenings out (ref = fewer than 3)
Three or more evenings out/week	1.48	<.001	1.33	<.001
Truancy (ref = no cutting class in past month)
Any classes cut in past month	1.88	<.001	1.64	<.001
Illicit drug use other than marijuana (IOTM) (ref = no past 12-month use)
Any past 12-month IOTM use	6.97	<.001	4.04	<.001
Cohort (ref = 2006–2016)
1976–1985	0.91	0.042	0.77	<.001
1986–1995	0.60	<.001	0.42	<.001
1996–2005	0.84	<.001	0.75	<.001

Note: Unweighted N = 84,805. All covariates were entered simultaneously and included missing data indicators; estimates for missing indicators not shown. Bold entries represent associations significant at p < .01.

^aSAM = simultaneous alcohol and marijuana use.

^bARR = Adjusted risk ratio.