Table 4. Adjusted 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
	Adjusted OR (95% CI)	p-value	Adjusted OR (95% CI)	p-value
Grade
7th–9th grade (middle school)	1.000 (reference)		1.000 (reference)
10th¬12th grade (high school)	0.735 (0.605 to 0.892)	0.002	1.147 (0.923 to 1.427)	0.216	1.561 (1.166 to 2.090)	0.003
Sex
Male	1.017 (0.837 to 1.236)	0.864	1.361 (1.087 to 1.705)	0.007	1.338 (0.994 to 1.802)	0.055
Female	1.000 (reference)		1.000 (reference)
BMI*, kg/m2	1.023 (0.997 to 1.049)	0.090	1.029 (1.001 to 1.057)	0.040	1.006 (0.969 to 1.044)	0.758
Residence
Rural	1.000 (reference)		1.000 (reference)
Urban	0.934 (0.777 to 1.124)	0.471	1.167 (0.941 to 1.447)	0.159	1.249 (0.941 to 1.659)	0.124
Current smoking	3.876 (3.066 to 4.900)	<0.001	1.969 (1.385 to 2.798)	<0.001	0.508 (0.333 to 0.775)	0.002
Depression	2.609 (2.158 to 3.156)	<0.001	2.827 (2.281 to 3.504)	<0.001	1.084 (0.813 to 1.443)	0.583
Highest educational level of parents
College or higher	1.000 (reference)		1.000 (reference)
High school or lower	0.911 (0.696 to 1.193)	0.500	0.757 (0.563 to 1.017)	0.065	0.831 (0.557 to 1.240)	0.364
Economic level
High	1.000 (reference)		1.000 (reference)
Middle-high	0.538 (0.397 to 0.729)	<0.001	0.846 (0.587 to 1.220)	0.371	1.572 (0.977 to 2.530)	0.062
Middle	0.559 (0.422 to 0.741)	<0.001	0.809 (0.568 to 1.151)	0.239	1.447 (0.921 to 2.273)	0.109
Middle low	0.837 (0.592 to 1.184)	0.314	1.042 (0.668 to 1.624)	0.857	1.245 (0.709 to 2.187)	0.446
Low	2.128 (1.421 to 3.187)	<0.001	2.430 (1.425 to 4.143)	0.001	1.142 (0.585 to 2.230)	0.698
School performance
High	1.000 (reference)		1.000 (reference)
Middle-high	0.756 (0.550 to 1.039)	0.084	0.852 (0.593 to 1.224)	0.386	1.127 (0.696 to 1.825)	0.627
Middle	0.873 (0.644 to 1.182)	0.378	0.753 (0.525 to 1.081)	0.124	0.863 (0.538 to 1.383)	0.539
Middle-low	0.745 (0.539 to 1.031)	0.076	1.010 (0.702 to 1.453)	0.958	1.356 (0.833 to 2.207)	0.221
Low	0.976 (0.689 to 1.382)	0.890	0.808 (0.522 to 1.250)	0.338	0.828 (0.474 to 1.447)	0.507

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).