Abstract: Objective To investigate the changes and influencing factors of mobile phone addiction among adolescents before and after the COVID-19 epidemic. Methods From December 6 to 20, 2019, and March 20 to 28, 2020, 3 124 students from a junior college, a secondary vocational school, and a high school in a city of Guangdong Province were surveyed by questionnaire. The changes in mobile phone addiction before and after the epidemic were compared based on propensity score matching, and a nomogram of mobile phone addiction among adolescents was constructed based on multivariate logistic regression. Results After propensity score matching, 1 236 students were matched before and after the epidemic respectively. The score of the Mobile Phone Addiction Tendency Scale （MPATS） for adolescents during the epidemic period was （39.28±10.03）, which was higher than that before the epidemic （37.03±10.45） （P<0.01）. The scores of MPATS during the epidemic period were higher in adolescents of different genders, different places of origin, non-only children, secondary school students, and with monthly living expenses less than 1 000 yuan than before the epidemic （P<0.01 or P<0.05）. Multivariate logistic regression analysis showed that urban students （OR=1.45）, secondary school students （OR=2.06）, often stay up late surfing by mobile phone （OR=2.36）, always stay online longer than expected （OR=2.08）, monthly mobile internet costs more （OR=1.47, 1.44, 2.25） increased the risk of mobile phone addiction among adolescents, while shorter daily accumulated time on mobile phone internet （OR=0.66, 0.70） reduced the risk of mobile phone addiction among adolescents. Based on the above factors, a nomogram model of adolescent mobile phone addiction risk was constructed, with AUC=0.72. Conclusions Compared with before the epidemic, the score and proportion of adolescents with mobile phone addiction increased during the epidemic period. The factors affecting adolescents with mobile phone addiction include their place of origin, education level, staying up late, online time, monthly spending on mobile phone internet, and daily accumulated time on mobile phone internet. Intervention measures should be taken to prevent the excessive use of mobile phones from causing adverse effects on adolescents.

Key words: COVID-19, Mobile phone addiction, Influencing factor, Propensity score matching, Nomogram