OBJECTIVETo describe the prevalence and relationship between screen time and sub-health status among middle school students in weekdays and weekends.

METHODSWith multistage stratified random cluster sampling, 14 400 students from junior and senior middle schools in 288 classes of 30 schools in 4 cities( Shenyang, Chongqing, Xinxiang, Guangzhou) were investigated in October, 2011. A total of 13 817 valid questionnaires were retained for analysis. Survey content includes general demographic information, screen time, sub-health state. Logistic regression model was used to analyze the relationship between screen time and sub-health status.

RESULTSThe screen time among middle school students > 2 h/d on weekdays and weekends were 15.1% (2 085/13 817) and 58.5% (8 077/13 817) , respectively. Among them, the boys' screen time > 2 h/d on weekdays and weekends were 17.9% (1 187/6 644) and 61.3% (4 070/6 644), which were higher than girls (12.5% (898/7 173), 55.9% (4 007/7 173) )(χ² values were 76.95 and 41.35, respectively. P < 0.01). The prevalence of physical sub-health status, psychological sub-health status and sub-health status were 24.8% (3 431/13 817), 21.7% (2 997/13 817) and 22.1% (3 051/13 817), respectively. Among them, the girls' prevalence of physical sub-health status, psychological sub-health status and sub-health status were 26.0% (1 863/7 173), 22.9% (1642/7 173) and 23.1% (1 658/7 173) ), respectively, which were higher than boys' (23.6% (1 568/6 644), 20.4% (1 355/6 644) and 21.0% (1 393/6 644)) (χ² values were 10.39, 12.66 and 9.25, respectively. P < 0.05). The senior students' prevalence of physical sub-health status, psychological sub-health status and sub-health status were 31.6% (2 176/6 884) , 28.3% (1 946/6 884) and 28.9% (1 990/6 884), respectively, which were higher than junior students' (18.1% (1 255/6 933), 15.2% (1 051/6 933) and 15.3% (1 061/6 933)) (χ² values were 337.65, 349.46 and 371.54, respectively, P < 0.05). After adjusting on demographic characteristics, compared with screen time ≤ 2 h/d on weekday, screen time > 2 h/d on weekday was significantly associated with physical sub-health status, psychological sub-health status and sub-health status (OR (95% CI): 1.39 (1.25-1.55), 1.62 (1.45-1.81) and 1.59 (1.43-1.78)). And compared with screen time ≤ 2 h/d on weekend, screen time > 2 h/d on weekend was also significantly associated with physical sub-health status, psychological sub-health status and sub-health status (OR(95% CI):1.49 (1.37-1.61), 1.81 (1.66-1.98), and 1.71 (1.57-1.87)).

CONCLUSIONThe rate of the screen time > 2 h/d and the detection ratio of sub-health among the middle school students in Shenyang, Chongqing, Xinxiang, Guangzhou in 2011 were high. Screen time >2 h/d on weekdays or weekends was a risk factor for sub-health status.