“…The results of another study on PIU also showed that the most strongly correlated psychosocial indicators of wellbeing with negative outcomes of the Internet use were loneliness and low self-esteem (Caplan, 2002). In the related literature, there are numerous studies showing that both loneliness (e.g., Boomsma, Willemsen, Dolan, Hawkley, & Cacioppo, 2005;McGuire & Clifford, 2000) and selfesteem (e.g., Kendler, Gradner, & Presscott, 1998;Raevuori et al, 2007) have a genetic component. Moreover, as mentioned earlier, it is argued that comorbidity of two disorders may indicate the casual relationship and/or common etiology shared by them (e.g., Mueser et al, 1998).…”