Table 1.

Chi-square comparison of predictor variables comparing students who responded to the questions about age of substance use initiation (Complete Case) compared to those who did not respond or who indicated “I don't know” (Missing/Don't Know).

Variable	Levels	Complete case		Missing/don't know		Chi-Sq
		n	%	n	%
Sex	Female	17,953	51%	2043	39%	<0.0001
	Male	17,268	49%	3161	61%
Data collection year	2012	4906	14%	508	10%	<0.0001
	2013	8579	24%	1218	23%
	2014	7539	21%	1152	22%
	2015	7179	20%	1227	24%
	2016	7018	20%	1099	21%
Ethnicity	White	27,898	79%	3740	72%	<0.0001
	Black	1604	5%	413	8%
	Asian	2305	7%	381	7%
	Indigenous	1029	3%	208	4%
	Latin American/Hispanic	866	2%	152	3%
	Other/mixed	1519	4%	310	6%
Weekly spending money	Zero	3876	11%	600	12%	<0.0001
	$1 to $20	5838	17%	802	15%
	$21 to $100	10,787	31%	1417	27%
	More than $100	11,277	32%	1664	32%
	Don't know	3443	10%	721	14%
Current smoker status	Non-smoker	29,720	84%	4017	77%	<0.0001
	Current smoker	5501	16%	1187	23%
Current drinker status	Non-drinker	17,556	50%	2236	43%	<0.0001
	Current drinker	17,665	50%	2968	57%
Current marijuana user status	Non-user	27,231	77%	3585	69%	<0.0001
	Current user	7990	23%	1619	31%