Jung and Ha has studied about the effects of stress and
emotional expression that affect smart phone addiction
among elementary school students [4]. In this research, they
found out that the higher the stress related to studying and the
negative emotional expression was, the higher the smart
phone addiction rate was. Kang and Park developed smart
phone addiction rating scale and verified it [22]. As a result,
smart phone addiction and depression, anxiety, impulsiveness,
and lack of control showed significant relationship. Lee said
that the factor that affects smart phone addiction is habitual
overuse due to smart phone's convenience and playfulness,
which leads to life problems [3].