Associations of excessive smartphone duration and unlock frequency with non-suicidal self-injury in college students

Table 3 Gender-specific association between smartphone use and non-suicidal self-injury

Smartphone use	Categories	OR (95%CI)1		P value for interaction
		Male	Female
Smartphone duration, continuous variable	Per 21 hours/week	1.19 (1.06, 1.33)	1.14 (1.05, 1.23)	0.67
Smartphone duration, categorical variable	0-21 hours/week	1 (reference)	1 (reference)	0.03
	21-42 hours/week	0.90 (0.50, 1.59)	1.40 (0.89, 2.17)
	42-63 hours/week	0.82 (0.47, 1.40)	1.72 (1.20, 2.50)
	≥ 63 hours/week	1.71 (1.11, 2.68)	1.64 (1.17, 2.34)
	Ptrend value	0.011	0.007
Number of smartphones unlocks, continuous variable	Per 50 times/week	1.02 (0.10, 1.04)	1.04 (1.02, 1.05)	0.20
Number of smartphones unlocks, categorical variable	0-50 times/week	1 (reference)	1 (reference)	0.17
	50-150 times/week	0.71 (0.43, 1.19)	1.29 (0.90,1.85)
	150-400 times/week	1.08 (0.65, 1.81)	1.60 (1.11, 2.32)
	≥ 400 times/week	1.08 (0.65, 1.82)	1.99 (1.39, 2.88)
	Ptrend value	0.232	< 0.001

¹These analyses were adjusted for grade, race, registered permanent residence, siblings, parental educational attainment, current smoking, current drinking, physical activity, rational diet, family disasters, hospitalization experience, failed exams, and failed relationships.

OR: Odds ratio; CI: Confidence interval.