Table 3. Crude OR difference in pandemic-related factors associated with substance use among Korean youth in KYRBS, 2019 versus 2021

Variables	Pre-COVID-19 pandemic (n=468)		COVID-19 pandemic (n=354)		Ratio of OR† (95% CI)	p-value
	Crude OR (95% CI)	p-value	Crude OR (95% CI)	p-value
Grade
7th–9th grade (middle school)	1.000 (reference)		1.000 (reference)
10th¬12th grade (high school)	0.947 (0.789 to 1.137)	0.560	0.785 (0.637 to 0.968)	0.023	0.829 (0.628 to 1.094)	0.186
Sex
Male	1.091 (0.909 to 1.309)	0.350	1.351 (1.092 to 1.671)	0.006	1.238 (0.936 to 1.639)	0.135
Female	1.000 (reference)		1.000 (reference)
BMI*, kg/m2	1.029 (1.004 to 1.055)	0.023	1.041 (1.014 to 1.068)	0.003	1.012 (0.976 to 1.049)	0.526
Residence
Rural	1.000 (reference)		1.000 (reference)
Urban	0.957 (0.797 to 1.149)	0.640	0.843 (0.681 to 1.044)	0.117	0.881 (0.665 to 1.167)	0.377
Current smoking	4.740 (3.818 to 5.886)	<0.001	2.815 (2.013 to 3.936)	<0.001	0.594 (0.398 to 0.885)	0.010
Depression	0.332 (0.276 to 0.398)	<0.001	2.942 (2.386 to 3.627)	<0.001	8.861 (6.710 to 11.703)	<0.001
Highest educational level of parents
College or higher	1.000 (reference)		1.000 (reference)
High school or lower	1.024 (0.789 to 1.330)	0.858	0.864 (0.648 to 1.152)	0.320	0.844 (0.572 to 1.244)	0.391
Unknown	1.187 (0.967 to 1.458)	0.101	0.994 (0.787 to 1.255)	0.958	0.837 (0.614 to 1.143)	0.263
Economic level
High	1.000 (reference)		1.000 (reference)
Middle-high	0.491 (0.365 to 0.660)	<0.001	0.335 (0.202 to 0.558)	<0.001	0.682 (0.379 to 1.228)	0.203
Middle	0.509 (0.390 to 0.664)	<0.001	0.268 (0.169 to 0.424)	<0.001	0.527 (0.310 to 0.896)	0.018
Middle low	0.890 (0.641 to 1.234)	0.484	0.250 (0.160 to 0.389)	<0.001	0.281 (0.162 to 0.488)	<0.001
Low	2.877 (1.974 to 4.193)	<0.001	0.376 (0.225 to 0.628)	<0.001	0.131 (0.069 to 0.247)	<0.001
School performance
High	1.000 (reference)		1.000 (reference)
Middle-high	0.663 (0.486 to 0.904)	0.009	0.811 (0.568 to 1.158)	0.248	1.223 (0.763 to 1.962)	0.403
Middle	0.782 (0.586 to 1.045)	0.097	0.740 (0.523 to 1.047)	0.089	0.946 (0.602 to 1.487)	0.811
Middle-low	0.803 (0.591 to 1.091)	0.161	1.110 (0.787 to 1.567)	0.551	1.382 (0.872 to 2.192)	0.169
Low	1.557 (1.130 to 2.145)	0.007	1.152 (0.765 to 1.735)	0.497	0.740 (0.440 to 1.244)	0.256

BMI, body mass index; CI, confidence interval; OR, odds ratios
Body mass index was calculated as weight in kilograms divided by height in meters squared.
Ratio of odds ratios was calculated as OR_{during-pandemic} divided by OR_pre-pandemic.
The ratio of odds ratios was calculated for one unit increase in body mass index (1 kg/m²).
Numbers in bold indicate a significant difference (p <0.05).