A. Antecedents
1) Parental variables Just as family's effect on children's game addiction is significant [22], family's effect on children's smart phone addiction is also substantial. Parental variables that affect smart phone addiction are parents' education, age, income, whether parents are working together, raising attitude, attitudes towards smart phone, and addiction tendency. In many studies, the lower the parents' income and education [18] were, the higher the possibility of children having problems [27] was. When parents' education is lower, knowledge about seriousness of smart phone addiction is also lower, so it is easy to give smart phone to their children, resulting in higher smart phone addiction rate. Parents with poor income cannot afford expensive smart phone, so their children's smart phone addiction rate might be low. However, adults' smart phone adoption rate has reached almost 90%, and non-adoption group is limited to old-aged group, so almost all low income parents have smart phones. They lack resources to raise their children, so they easily let their children use smart phones same as game addiction of children [26]. Therefore, the lower the parents' income is, the higher their children's smart phone addiction rate is. Smart phone is a device which young people easily use and adopt pervasively. Younger parents tend to have more generous adoption attitudes about smart phone, and higher usage frequency. As a result, their children have higher chance of contact and using smart phones, therefore having higher smart phone addiction rate like internet addiction of children [7]. Children from dual-income family have longer time alone and because of lack of parent's amount of time to take care of their children; they are generous about the requirements of their children [11]. Therefore, they easily let their children use smart phones, resulting in higher smart phone addiction rate. Types of parenting can be divided into authoritarian, permissive, and responsive [28]. Authoritarian is one-way and rigorous way of raising children, strictly controlling their children. Permissive is full of affection, inconsistent, and laissez faire. On the other hand, responsive is respecting children's autonomy, being consistent. Children from authoritarian parents lack their own goals or judgments, exclusive and aggressive. Children from permissive parents are impulsive, selfish, stubborn, and hysteric. Children from responsive parents have clear goals and decision of their own, self-regulated and having high self-trust, they are likely to have positive and harmonious interpersonal relationships. Therefore, permissive parents are most likely to have children with higher smart phone addiction rate [27]. In addition, parents' attitudes towards smart phone or usage behaviors are likely to have influenced children's smart phone addiction rate same as internet addiction of children [9]. When parents have more positive attitudes towards smart phone, they let their children use smart phone more easily, resulting in higher rate of smart phone addiction. Furthermore, if parents themselves are heavy users of smart phone or addicted to it, their children have higher chance to be exposed to smart phones, resulting in higher smart phone addiction rate.
2) Child variables Child variables affecting child smart phone addiction are child's age, gender, number of siblings, and whether they attend education institutions or not. The lower child's age is, mental development is incomplete and easily immersed, having higher possibility of smart phone addiction [10]. In addition, boys tend to have more curiosity about tools and needs for trial. Also, boys tend to be more distractive and lack of self-control [14], so they have higher possibility of addiction to smart phone. While higher number of siblings means higher possibility of interacting with other people, lower number of siblings means more time spending alone, resulting in higher possibility of addiction to digital tools like smart phones [15]. In addition, when a child attends education institutions like preschool or kindergarten, they are likely to be under teacher's control and have more time to interact with peers, resulting in lower smart phone addiction rate. On the other hand, children not attending any education institutions have more time alone at home and because of lack of parents' resources, they have higher possibility of smart phone addiction.