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The smartphone has rapidly developed over recent years, with use becoming widespread and an established part of daily life throughout the world. According to the Ministry of Internal Affairs and Communications of Japan, 94.5% of individuals in their 20s in 2017 were smartphone owners (Ministry of Internal Affairs and Communications, 2018). In conjunction with this rapidly growing popularity, various applications, including those associated with social networking services (SNS) and online gaming, have been developed for use with smartphones, thus allowing the Internet to become more accessible. At the same time, problematic smartphone use and patterns of addiction are routinely reported.
The term addiction is not only applied to abuse of drugs or substances, but also gambling, gaming, Internet access, mobile phone usage, and other behavioral addictions (Kwon, Lee, Won et al., 2013). Griffiths reported elements related to Internet addiction, such as tolerance, withdrawal symptoms, and recurrence (Griffiths, 1998), and smartphone addiction has been found to be similar in many aspects to Internet addiction (Kim, 2013; Demĭrcĭ, Akgӧnül, & Akpinar, 2015). On the other hand, there are also some important differences, such as easy portability, real-time Internet access, and direct communication features, offered by smartphones (Kim, Jang, Lee, Lee, & Kim, 2018). Although official diagnostic criteria for smartphone addiction have not been presented, it is generally defined as overuse of a smartphone to the extent that it disturbs the daily life of the user (Demĭrcĭ, Akgӧnül, & Akpinar, 2015). In reference to previous studies of Internet and smartphone addictions, the present authors defined smartphone addiction in terms of the following aspects: overuse, tolerance, withdrawal, cyber life orientation, difficulty with performing study or work, and physical symptoms caused by smartphone use (Ezoe, Iida, Inoue, & Toda, 2016).
Smartphone addiction, particularly among adolescents, has become an important problem in Japanese society. The Cabinet Office in Japan recently reported that 39.4% of high school students were accessing the Internet by means of a smartphone for more than 4 hours each day in 2018 (Cabinet Office, 2019). Although scant findings concerning hours of smartphone use by Japanese university students have been presented, we previously reported that the mean daily smartphone use on weekdays by that population was 3.1 ± 1.8 hours, while that during holidays was 4.1 ± 2.1 hours (Ezoe, Iida, Inoue, & Toda, 2016).
Psychiatric symptoms, particularly depression, have been reported to be associated with smartphone addiction in many countries. The term depression, which refers to a spectrum of disorders, implies progression from a temporary depressed mood induced by undesirable events in daily life to a serious major depressive disorder (Rubin & Carroll, 2010). According to the American Psychiatric Association (American Psychiatric Association, 2013), a common feature of all depressive disorders including major depressive disorder is “the presence of a sad, empty, or irritable mood, accompanied by somatic and cognitive changes that significantly affect the individual’s capacity to function”. Some related symptoms can be observed by a trained clinician, while others are felt only by the subject, though can be assessed by use of a self-rating questionnaire. In the present study, depression in healthy university students in Japan was examined along with its association with smartphone usage.