Who Is the Chief Culprit, Loneliness, or Smartphone Addiction? Evidence from Longitudinal Study and Weekly Diary Method

It is common for adolescents to feel lonely, and many previous studies have already found that loneliness is closely related to smartphone addiction (SPA). However, whether smartphone addiction leads to loneliness or loneliness leads to smartphone addiction, there is a lack of strong empirical research support. Therefore, based on the compensatory internet use theory and the digital goldilocks hypothesis, this study explored the causal and correlational relationship between loneliness and smartphone addiction by using a longitudinal study and a weekly diary method at the trait and state level. In the first study, 906 adolescents (Mage = 11.20, SDage = 1.65, 51% females) were recruited to participate in the 1-year longitudinal study, and a cross-lagged model of loneliness and smartphone addiction was constructed to explore the causal relationship between them. In the second study, 117 adolescents (Mage = 15.44, SDage = 0.53, 66% females) were measured 7 times by the weekly diary method; the correlational relationship between loneliness and smartphone addiction was explored by building a hierarchical linear model (HLM). The results showed that: (1) trait loneliness positively predicted smartphone addiction among adolescents; (2) smartphone addiction could not predict loneliness; (3) loneliness positively affected smartphone addiction at the state level; (4) smartphone addiction also positively affected the weekly loneliness at the state level. This study revealed the causal relationship between trait loneliness and smartphone addiction and the relationship between loneliness and smartphone addiction at the state level. The present study also expands the understanding of the causal relationship between smartphone addiction and loneliness from two theoretical perspectives, and it also has practical significance for preventing the phenomenon of smartphone addiction among adolescents.