Life-Stage Differences in the Associations Between Solitude Orientation and Loneliness-Related Outcomes: Solitude Orientation as a Non-Defining Feature of Hikikomori

Abstract This study examined whether the associations between solitude orientation, loneliness, and social isolation differ across life stages, including individuals with hikikomori. A cross-sectional questionnaire survey was conducted with 84 participants equally distributed across four groups: hikikomori, young adults, adults, and older adults (n = 21 each). Solitude orientation (Preference for Solitude Scale), loneliness (UCLA Loneliness Scale), social isolation (Lubben Social Network Scale), and depressive symptoms (Beck Depression Inventory) were assessed. Bayesian linear regression models were used to examine group-specific associations, and Firth penalized logistic regression was conducted to identify factors associated with hikikomori status. The associations between solitude orientation and loneliness-related outcomes differed across groups. In the adult group, higher solitude orientation was associated with lower loneliness and with lower social isolation. In the hikikomori group, solitude orientation was positively associated with social isolation but was not significantly associated with loneliness. In the young group, solitude orientation was not significantly associated with either loneliness or social isolation. In the older group, solitude orientation was not significantly associated with loneliness but tended to be positively associated with social isolation, suggesting a link with smaller social networks in later life. In logistic regression analyses, social isolation and depressive symptoms were significantly associated with hikikomori status, whereas solitude orientation was not. These findings indicate that the meaning of solitude orientation differs depending on life stage and social context and that solitude orientation itself is not a defining characteristic of hikikomori.