A systematic review on correlates of screen-viewing show that screen-viewing is not equally distributed across social and demographic groups [12]. A Norwegian study found differences in screen time activity between the sexes [13], that screen time increase with age [13], and that higher parental education is related to less time spent on screen activities [13]. Results from a recent study among Norwegian adolescents showed that more screen time increased the risk of overweight and obesity [13] and there was also a clear link between overweight and social class; the prevalence of overweight and obesity was higher in children of parents with lower education [13]. In Norway, the prevalence of overweight among 11-year olds is 14–16% [13-15] and the prevalence of obesity is about 1–2% [13-15], which is lower than for other European countries, according to results from the ENERGY-project [15]. The prevalence of obesity is increasing with age and about 20% of Norwegian adults are classified as obese [16]. Among obese ethnic Norwegian adolescents, the prevalence of metabolic syndrome is 30% [17]. Compared with other European countries, like Hungary and Greece, the Norwegian adolescents have a more favourable cardiometabolic risk profile [18]. There are no studies presenting secular trends of overweight for 11-year-olds in Norway; however, data on 9-year-olds show an increase of overweight children from 2008 to 2010 in Norway [19]. With the increasing number of overweight children, supervising risk factors like sedentary behaviour is important.

In 2001 The American Academy of Pediatrics recommended that paediatricians should recommend that parents limit children’s total media time to no more than 2 hours a day [20]. This recommendation has been implemented in national recommendations in Australia [21] and in the USA [20]. Although there are no such recommendations in Norway, there have been some initiatives to increase physical activity in children and adolescents [22]. Since 2001 the Directorate of Health has started surveillance of activity and inactivity in national studies. They have implemented an action plan on physical activity [23]. This action plan focused on active leisure time, active everyday life and active environment by encouraging the experience of outdoor life, securing areas for public sojourn and travel, and promoting opportunities for physical activity in kindergartens, schools and at work. The action plan did not specifically focus on reducing screen time; however, by increasing active leisure time, a reduction in screen time might be observed. A study among Norwegian children found clear relations between physical activity (PA) and sedentary behaviour, where high PA was correlated with less screen time [2]. However, some researchers have found that PA and sedentary behaviour represent different paradigms [24] and that preventive action against metabolic risk in children may need to target TV viewing and PA separately [25].

Few studies have assessed the longitudinal pattern of screen time activity [26-29]. A recent American study showed that levels of screen time activity were stable in a nationally representative sample of children aged 9–13 year olds from 2001–2006 [26]. An Australian study found that from 1997 to 2001 there was a decrease in number of children who met the guideline of less than 2 hours of screen time activity [27]. Results from the Health Behaviour in Schoolaged Children (HBSC) study showed that there was an increase in hours spent on personal computers (PC) per week in Norwegian 6^th, 8^th and 10^th grades from 1997 to 2005 [30]. Further results showed that there was a decrease in time spent in front of TV from 1997 to 2005 [30]. No study has assessed time changes in screen time activity in Norwegian children and adolescents in the same region after 2005. Cross sectional studies have shown that 36-42% of Norwegian 6–8 year olds and 56-65% of Norwegian 9–11 year-olds [13] exceed the 2 hour screen time per day recommendation. This is line with other countries where many children do not meet the recommendations [31]. Recent results from the ENERGY-project show that Norwegian boys and girls spend 168–196 minutes per day in front of screens [15].

Exploring the differences in screen time activity further, Table ​Table11 shows that in 2008 compared with 2001 a higher proportion of participants reported spending 0.5-1 hour a day (41% vs 33%) and a lower proportion reported to spend 2–3 hours/day on screen time activity (33% vs 35%).

Few studies have described time change in screen time activity in children during the past decade. Some previous studies have reported an increase in the number of children exceeding the recommended screen time per day [28,29,35], while a recent American study found that time spent on screen time activities was stable from 2001 to 2006 among children and adolescents and that more than 75% met the guidelines of not exceeding 2 hours a day [26]. In Norway, the HBSC-study showed an increase in time spent on personal computers and a decrease in time spent watching TV in adolescents from 1997 to 2005. The reduction found in total screen time activity in the present study is surprising; thus, exploring the limitations with the question posed is warranted. In our study, participants were asked to report total time spent on all screen time activity. From 2001 to 2008, there has been an increase in computer usage in Norway, e.g., the proportion having a PC at home has increased from 75% to 90% in the general Norwegian population [36]. This change might have led the participants to interpret the question differently in 2008 compared with 2001. The HBSC-study changed the question used in 2005 because of new screen activity use and divided the question regarding PC use into the two categories of a) TV-games, PC-games and b) chatting and surfing. Having such a wide question as in the present study might have led to underreporting of newer screen time activities in 2008 compared with 2001, such as homework, chatting, internet gaming, use of cell phones, etc. The general reduction found in the present study might also in part be a result of the already mentioned initiatives from health authorities on increasing physical activity to limit sedentary behavior. National studies in adults show an increased knowledge regarding the negative effects of too much screen time activity and the benefits of increased physical activity [22], supporting the possibility that these initiatives might have had a positive impact. In addition, the observed differences in parental age and education between 2001 and 2008 might also partly explain the decrease, as older parents may be more traditional in their approaches to child rearing and may let their children spend less time on video games and computers [37].

In line with the above discussion, it is interesting to note that the observed changes in screen time activity were more evident among specific socio-demographic groups. There was a marked reduction in screen time activity among those with highly educated parents. This is consistent with the results of previous research [3,38-40], showing that parents with higher education are more likely to follow health recommendations and act on health authority initiatives than those without higher education. Several studies find that maternal educational level is consistently inversely associated with children’s television viewing [38].

Most studies find, like the present one, that older children are more likely than younger ones to spend more than 2 hours daily on screen time activities [2,12,31,38]. The marked reduction among 6^th graders may reflect several aspects. First, the younger the children are, the more likely they are to be supervised and have strict rules regarding screen time activities [31]. Second, demands to use computers for home work are more frequent with increasing age, and older children tend to have greater access to media sources than do younger children [31].

The present results suggest that boys spend more time than girls on screen time activities. This is comparable to findings from other studies investigating sex differences in screen time activities [2,31]. However, studies including new sedentary behaviors, such as talking on the phone, texting, and instant messaging, find that girls are more likely to report more time spent on these activities than boys [41]. Other studies have also found that boys report being engaged in more physical activity compared with girls [42], suggesting that girls spend their leisure time doing other activities than physical activity and screen based activity. In the present study, we observed no differences in screen time activity between sexes over time.

Strengths and limitations: This study includes two cross-sectional surveys seven years apart in a well-defined population from two Norwegian counties. It included a high number of schools, and the participation rate for the children was high. The same question, with proven acceptable reliability in this age group, was used to measure screen time activity exposure at both time points.

However, it is a clear limitation of this study that the assessment tool used for screen time activity included one question only. Thus, we were not able to assess time spent on different activities such as TV-viewing, gaming, and internet based activities. This might have led to an underreporting of newer screen time behaviours in 2008 compared with 2001. Acceptable test-retest reliability of the question was found, indicating that the age group had a stable understanding of what screen time activities are and that the question assessed this activity acceptably. Future studies should, however, include detailed questions of screen activities to identify what activities are the main sources of screen time. A further limitation is that weight status was not included in this study. Some results suggest that overweight children spend more time on screen time activities and this relationship could not be assessed in this paper.