South Korea has a fairly high smartphone penetration rate. In 27 countries worldwide, the average percentage of smartphone users is about 76%, whereas, in Korea, smartphone users comprise 95% [1]. The proportion of Korean teenagers who own a smartphone continues to increase, reaching 89.7% in 2019 and 94.4% in 2020 [2]. As smartphone use becomes more ubiquitous, the risk of overdependence is also increasing annually. Across the risk groups by age, the ratio of the teenage group is the highest, compared to other age groups [2,3]. The smartphone overdependence ratio in school-aged children is about 30%, which is higher than that in preschool children (27%) and adults (22%) [3].

During the late school age, the frontal lobe has not yet developed [4]. This issue may make children highly impulsive children are highly impulsive and lack control and are at high risk of dependence on technology like a smartphone or the internet [3]. Children's excessive use of smartphones causes various health issues. When a child spends a lot of time using a smartphone, it can cause neck and spine flexion [5]. and visual impairment [6]. Additionally, the risk of obesity, sleep disorders, and poor physical activity increases [7,8]. Technology like internet and smartphone addiction also affects brain development, causing children to become distracted and have a shorter attention span, increasing the likelihood of attention deficit hyperactivity disorder [8,9]. Furthermore, children who constantly use smartphones are at an increased risk for depression, anxiety disorder, and suicidal ideation [9]. To preserve children’s health into adolescence and adulthood, it is necessary to identify the factors that influence smartphone dependence in children, as they are more prone to overuse.

Several studies identify factors related to smartphone dependence [10-13]. Factors such as impulsivity and lack of self-control were found to be internal individual factors highly correlated with smartphone dependence [11,12]. Recently, grit has gained attention as an internal individual factor related to technology dependence [14]. Grit refers to the ability to manage impulsivity and self-control in connection with addiction, as well as the ability to maintain perseverance and passion in the long term to achieve goals [15]. Grit is a variable that allows for a better understanding of an individual's internal characteristics associated with dependence and addiction. Grit is an acquired ability that can be learned through practice and experience [16], so it can serve as a protective factor against addiction. However, few studies have examined grit as a factor in children's dependence. Therefore, the present study selected grit as an internal factor of smartphone dependence.

The family is an external factor that has a significant influence on children's behavior. Children who lack support at home or have poor familial relationship become preoccupied and dependent on the relationship they create online and are more susceptible to harmful behaviors and addiction [13,17]. Among family-related factors, family strengths are qualities that emphasize the well-being of the family and can be used as an index to identify family functions such as familial relationship, emotional support, and communication [18]. Therefore, this study selected family strengths as an external factor in children's smartphone dependence.

Several studies to identify factors of smartphone dependence have been conducted on young adolescents attending middle or high school [10,11,13]. Studies on children aimed at identifying both internal and external factors of smartphone dependence are rare. Therefore, this study aimed to investigate grit as an internal factor and family strength as an external factor that would be significant factors associated with smartphone dependence among late school-aged children. This study’s findings are expected to provide a basis for interventions to help children avoid smartphone overdependence.

Of 218 respondents, 55% were female. As for smartphone usage duration, 47.3% of participants were more than 3 years. 57.3% of the participants used a smartphone for less than 2 hours a day. The main purpose of using a smartphone was to watch a video (37.2%), followed by social networking (26.6%) and games (22.5%) (Table 1). The mean scores for smartphone dependence by general characteristics are presented in Table 2. We found significant differences in smartphone dependence based on the smartphone usage hours per a day (t=-4.38, P<0.001) and the main purpose of usage (F=3.24, P=0.008). The overall smartphone dependence of the participants was 2.47 (±0.93) out of 6. The participants’ grit was 3.30 (±0.49) and family strengths was 3.99 (±0.68) out of 5. A significant negative correlation was observed between the participants’ smartphone dependence and grit (r=-0.56, P<0.001). The participants’ family strengths was also significantly and negatively correlated to the smartphone dependence (r=-0.32, P<0.001) (Table 3).

Table 4 shows the multiple regression statistics of factors influencing the smartphone dependence. In the model, the explanatory power was 38% (F=17.620, P<0.001) and smartphone usage time ≥2 hours per a day (β=0.198, P<0.001), gaming (β=0.215, P=0.046) or social networking (β=0.304, P=0.007) of the main purpose of smartphone usage and grit were significant factors associated with the levels of smartphone dependence.

This study was conducted to investigate grit as an internal factor and family strength as an external factor on the smartphone dependence of late school-aged children.

Grit exerts the most significant influence on smartphone dependence in children in this study, which means that the lower grit, the higher the smartphone dependence. This is in line with previous studies that have shown that grit has a significant factor on addictions [14,22]. This is because the grit is the ability to sustain effort over a long period to achieve a goal [15]; hence, a person with a high level of grit will continue to strive to reduce or avoid smartphone use, even if there are obstacles. People with a high level of grit self-regulate and control themselves to achieve their goals [15]. In other words, children with a high level of grit are better at managing and controlling smartphone use, so they are more resistant to overdependence. Given that grit is an acquired ability [16] and that childhood is a period when parental control begins to wane and inhibitory control, such as self-control and regulation, begins to improve [4], strengthening grit during childhood will help children avoid overdependence and achieve desired growth and development. Grit is also an important quality that contributes to the overall development and successful adaptation [16,21]. Therefore it is necessary to enhance the grit of late school-age children through educational interventions that have been found to be effective in promoting grit.

Children whose main purpose of smartphone usage is gaming or social networking have a higher level of dependence than children who use smartphone mainly for calling and messaging. Previous studies reported that engagement with social media or games may be a strong factor of dependence [10,13]. The reasons child smartphone users engage strongly with social media platforms or games may be to form friendships, have fun, and relieve stress [10]. Social media platforms and games allow them to build relationship better than is possible for them in real life, while also bringing them joy. These benefits give children a sense of belonging and help them relieve negative emotions such as depression and anxiety. This acts as a reward, further encouraging overdependence [10,13]. Therefore, offline activities from which rewards can be derived and that encourage physical activity and peer interaction are needed to meet children's needs.

Time spent on a smartphone was also found to be a factor of smartphone dependence. Previous studies have demonstrated that the longer the usage time, the higher the risk of technology addiction [13,23]. However, restricting usage, that is, forcibly limiting time spent on smartphones, is known to be ineffective against overdependence [24,25]. Therefore, as an alternative strategy, it is important to direct children toward spending more time on offline activities, rather than forcing them to refrain from using smartphones. Additionally, as previously mentioned, it is vital that children develop the ability to self-regulate and exercise self-control through mechanisms such as grit. Moreover, improving media literacy, which is the ability to exercise judgment and control concerning media use, will be more effective in relieving children's maladjustment problems caused by smartphone use [26].

In this study, the external factor, family strengths, was not significant. This may be attributable to the fact that although modern society incorporates many different types of families, the tools used in this study were developed based on a traditional nuclear family [18], so it may not reflect the behavior of different kinds of families. Future research that encompasses a range of family types is needed to measure family strengths more accurately. Furthermore, since the overall explanatory power of the model was rather low, external factors affecting smartphone dependence should be expanded. It is necessary to explore environmental factors surrounding children that affect smartphone dependence, such as parents' smartphone use time and patterns, relationships with friends. The present study showed that dependence is not associated with gender. Gender is known to be a major predictor of smartphone dependence, but some studies have proven otherwise [13]. According to previous studies, girls mainly use their phones for social media, while boys tend to play online games [13,17]. In other words, there are gendered differences in the purposes of smartphone use, which seem to cause differences in smartphone dependence. Additional research is needed to collect more evidence.