screen time , which is often used for assessing sedentary behaviors , is defined as the time adolescents spend on watching television ( tv ) , video games , and using a computer . however , most children and adolescents do not adhere to these guidelines as screen time in 79.5% of adolescents in brazil is more than 2 h / day . a cross - sectional study in barcelona also revealed that about 50% of students spend more than 2 h / day on watching tv . a total of 68.2% of boys and 61.7% of girls use computer more than 2 h / week . in this context , a cross - sectional study on 370 children in korea showed that screen time in about 46% of children is 12.9 h and in 8.9% is more than 3 h / day . a national study reported that approximately 33.4% and 53% of iranian students aged 618 years spend their time for watching tv or video on weekdays and on weekend , respectively , and about half of urban students and a quarter of rural students used a personal computer ( pc ) . unfavorable lifestyle habits of children and adolescents , especially sedentary behaviors , threat to health in this group , and the population is at risk for cardiovascular epidemics such as cardiovascular disease , hypertension , diabetes , and psychological disorders . in this context , evidence suggests that increased time watching tv was associated with an increase in obesity in children and adolescents . a number of studies reported the association between screen time and increased risk of metabolic syndrome or its components in children and adolescents . research has been done on factors related to screen time , and meta - analysis study showed that children with overweight and obesity had more risk for screen time more than 2 h compared to children with normal weight . data showed that high socioeconomic status ( ses ) , unhealthy eating habits , depression , and mental problems are related to screen time . most studies have studied the effect of factors related to screen time , while a few studies assessed separately the factors associated with time spent watching tv or using a computer . on the other hand , there is evidence about factors affecting screen time often in developed countries and in developing countries ; especially , our country has limited studies . this study aims to assess the factors associated with screen time in iranian children and adolescents . this study was performed as part of the fourth survey of the national schoolbased surveillance system entitled the  childhood and adolescence surveillance and prevention of adult noncommunicable disease  study . the participants of the present study were selected from elementary , intermediate , and high school by a cluster sampling method in 30 provinces of iran ( 48 clusters of 10 people in each province ) . totally , 13,486 students in the age range of 618 years were participants in this study . the students who did not have data about time spent watching tv and using computer were excluded from the study . ethical approval was obtained from the ethical committees , and participants signed informed consent after receiving explanation of the study protocols . data were obtained by the questionnaire of the world health organization - global student health survey that validity and reliability were assessed previously . ses was assessed through principal component analysis methods by some variables including parents education , parents occupation , possessing private car , school type ( public / private ) , type of home ( rented / private ) , and having pc in the home , which were summarized in one main component . the first tertile was defined as low , second tertile as moderate , and third tertile as high ses . ( 1 ) during the past week , on how many days were you physically active for overall 30 min per day ? ( 2 ) how much time do you spend in exercise class regularly in school per week ? the first tertile was defined as a mild , second tertile as a moderate , and third tertile as a severe . psychiatric distress included worry , depression , confusion , insomnia , anxiety , and aggression , and feelings of being worthless were assessed by seven questions . the screen time behavior of children was assessed by a questionnaire that asked the child to report the average number of hours per day spent watching tv / vcds , pc , and electronic games . screen time activity was categorized into two groups ( < 2 h / day and 2 h ) . to assess dietary habits , food frequency questionnaire was applied and nine items include sweets , salty / fatty snacks , soda , fruits , dried fruit , vegetables , sugar - sweetened drinks , milk , and fast food . five groups of foods were considered as unhealthy foods , including sweets , salty / fatty snacks , soda , sugar - sweetened drinks , and fast food . the first tertile was defined as a mild , second tertile as a moderate , and third tertile as a severe . height was recorded to the nearest 0.1 cm without shoes , and weight with minimal clothing with 0.1 kg accuracy using calibrated instruments . the data were analyzed by the stata software version 10.0 ( stata corp , college station , texas , usa ) . the categorical variables were presented as number ( % ) and continuous variables were summarized as mean ( standard deviation [ sd ] ) . logistic regression was performed to assess the association of independent variables with screen time in different models for adjusting potential confounders . data were obtained by the questionnaire of the world health organization - global student health survey that validity and reliability were assessed previously . ses was assessed through principal component analysis methods by some variables including parents education , parents occupation , possessing private car , school type ( public / private ) , type of home ( rented / private ) , and having pc in the home , which were summarized in one main component . the first tertile was defined as low , second tertile as moderate , and third tertile as high ses . ( 1 ) during the past week , on how many days were you physically active for overall 30 min per day ? ( 2 ) how much time do you spend in exercise class regularly in school per week ? the first tertile was defined as a mild , second tertile as a moderate , and third tertile as a severe . psychiatric distress included worry , depression , confusion , insomnia , anxiety , and aggression , and feelings of being worthless were assessed by seven questions . the screen time behavior of children was assessed by a questionnaire that asked the child to report the average number of hours per day spent watching tv / vcds , pc , and electronic games . screen time activity was categorized into two groups ( < 2 h / day and 2 h ) . to assess dietary habits , food frequency questionnaire was applied and nine items include sweets , salty / fatty snacks , soda , fruits , dried fruit , vegetables , sugar - sweetened drinks , milk , and fast food . five groups of foods were considered as unhealthy foods , including sweets , salty / fatty snacks , soda , sugar - sweetened drinks , and fast food . the first tertile was defined as a mild , second tertile as a moderate , and third tertile as a severe . height was recorded to the nearest 0.1 cm without shoes , and weight with minimal clothing with 0.1 kg accuracy using calibrated instruments . the data were analyzed by the stata software version 10.0 ( stata corp , college station , texas , usa ) . the categorical variables were presented as number ( % ) and continuous variables were summarized as mean ( standard deviation [ sd ] ) . logistic regression was performed to assess the association of independent variables with screen time in different models for adjusting potential confounders . the participation rate was 90.6% ( n = 13 , 486 ) ; 50.8% were boys , and 75.6% lived in urban regions . the mean ( sd ) age of participants was 12.47 ( 3.36 ) years . in total , 50.66% of students watched tv more than 2 h / day , 9.63% of those used a computer more than 2 h / day in their leisure time , and 18.62% of students had screen time more than 4 h / day . table 1 shows the demographic characteristics of students according to sex and age . in both sex groups , the frequency of watching tv ( more than 2 h ) , using computer ( more than 2 h ) , and screen time ( more than 4 h ) was significantly higher in the age group of 1318 years than age group of 612 years . in addition , the age group of 1318 years had more pc and higher ses than age group 612 years ( p < 0.001 ) . characteristics of study population according to sex and age : the caspian - iv study prevalence of psychiatric distress by sex is shown in table 2 . the results presented that significantly , the prevalence of psychiatric distress was higher in girls than boys ( p < 0.001 ) . prevalence of psychiatric distress by gender : the caspian - iv study table 3 presents the association of independent variables with screen time in logistic model . the results showed that older participants had significantly higher risk for higher watching tv , using computer , and screen time ( p < 0.001 ) . significantly , girls had less risk for using computer and screen time than boys ( p < 0.001 ) . students from high ses regions and students with unhealthy diet had greater risk for higher watching tv , using computer , and screen time ( p < 0.001 ) . overweight and obese students significantly had more risk for high watching tv . with the increasing number of children , the risk of watching tv significantly decreased ( p < 0.001 ) . participants with insomnia and aggression significantly had higher risk for higher using computer and screen time ( p < 0.001 ) . association of independent variables with screen time in logistic regression model : the caspian - iv study the findings of the present study showed that students with higher ses , unhealthy food habits , from urban areas , and older had higher risk for higher watching tv , using computer , and screen time . the findings of previous studies showed that there was a significant association between age increasing with screen time , which was consistent with our results . 's study indicated that age was positive associated with using computer , while no significant association was found between age and time spent watching tv . in the present study , no significant association was seen between sex and time spent watching tv , which was consistent with previous studies . data showed that boys had more risk for high screen time than girls , which was consistent with our results . the high level of screen time in boys may due to high using computer and video games , and on the other hand , in girls in addition to watching tv , other sedentary behaviors such as talking on the phone , listening to music , and reading were seen more than boys . the results of our study presented that students from urban regions had higher risk for watching tv , using computer , and screen time . a cross - sectional study in greece showed that living in urban is associated with high risk of watching tv . in urban regions , high access to cafenets , internet , computer games , and , on the other hand , increasing urbanization and decreasing access to safe environment for playing cause watching tv and using computer , which are the main entertainments of children and adolescents . in the current study , participants from high ses regions had higher risk watching tv , using computer , and screen time . high level of screen time in high ses level may due to great access to electronic devices , video games , and computer . the results of a study in columbia showed that factors such as working mother and income families were positively associated with access to electronic devices , tv , and computer in a child room . significant association between physical activity and time spent watching tv and screen time was found in our study . the results of studies have been inconsistent , but some data showed that watching tv and using computer may replace physical activity in children and adolescents . previous study indicated that low level of physical activity was related to increased time spent watching tv and using computer . in the present study , no significant association was found between family structure and time spent watching tv , using computer , and screen time . the results of our study were consistent with previous study . in our study , with increasing number of family 's children , the risk of watching tv decreased . the results of a cross - sectional study in barcelona showed that boys who live with both parents use media less than boys who live with one parent . data presented no significant association between weight and screen time , which was consistent with our results . while other studies showed that obesity was positively associate with increase of screen time , in our study students with overweight and obesity significantly had higher risk of increasing time spent watching tv . in addition , in our study , positive association was found between unhealthy eating habits and screen time . results of other studies showed that unhealthy eating habits were associated significantly with screen time . the findings of study in belgium showed that unhealthy eating habits such as high consumption of soda and chips in early adolescence predict the high screen time in early adulthood . data indicated that fast food consumption and eating junk food were associated with screen time and increasing time spent watching tv . in our study , students who had experience of worthlessness had high risk for increasing watching tv , and aggressive students had more risk for increased time spent watching tv , using computer , and screen time . data showed that depression was in related to time spent watching tv and video games . in the present study , there was no significant association found between depression and watching tv that may due to different data collection method . the study design was cross - sectional that not allowed to conclusion about causation . despite these limitations , main strength of the current study was large sample . findings show the association of age , ses , living area , eating junk foods , and some psychiatric distress with screen time , watching tv , and using computer during leisure time . effective interventions should consider the modifiable risk factors to reduce the screen time and its adverse health effects . the current study was funded by isfahan university of medical sciences ( project code : 294176 ) . the current study was funded by isfahan university of medical sciences ( project code : 294176 ) .
background : prolonged screen time is frequent in children and adolescents . implementing interventions to reduce physical inactivity needs to assess related determinants . 
 this study aims to assess factors associated with screen time in a national sample of children and adolescents.methods:this nationwide study was conducted among 14,880 students aged 618 years . 
 data collection was performed using questionnaires and physical examination . 
 the world health organization - global school health survey questionnaire was used . 
 logistic regression analysis was used to examine the relationship between demographic variables , socioeconomic status ( ses ) , family structure , physical activity , unhealthy eating habits , body mass index , and mental distress with screen time.results:the participation rate was 90.6% ( n = 13,486 ) , 50.8% were male , and 75.6% lived in urban areas . 
 mean ( standard deviation ) age of participants was 12.47 ( 3.36 ) years . 
 the ses , eating junk foods , urban residence , and age had significant association with screen time , watching television ( tv ) , and computer use ( p < 0.05 ) . with increasing number of children , the odds ratio of watching tv reduced ( p < 0.001 ) . statistically , significant association existed between obesity and increased time spent watching tv ( p < 0.001 ) . 
 girls spent less likely to use computer and to have prolonged screen time ( p < 0.001 ) . 
 participants in the sense of worthlessness were less likely to watch tv ( p = 0.005 ) . 
 screen time , watching tv , and using computer were higher in students with aggressive behaviors ( p < 0.001 ) ; screen time was higher in those with insomnia.conclusions:in this study , higher ses , unhealthy food habits , and living in urban areas , as well as aggressive behaviors and insomnia increased the risk of physical inactivity .