| Title of study | Year | Type of study | Country | Sample (N) | Findings |
| Hikikomori in Spain: A descriptive study [12] | 2015 | Descriptive | Spain | N = 164 | Hikikomori were predominantly young male, with the mean age at onset of hikikomori of 40 years old and a mean socially withdrawn period of 3 years. Only three people had no symptoms suggestive of mental disorder. Psychotic and anxiety were the most common comorbid disorders |
| Home visitation program for detecting, evaluating, and treating socially withdrawn youth in Korea [14] | 2013 | Case control | Korea | N = 41 vs N = 248 | Over 50% of hikikomori cases had either passive or indifferent relationships with peers and parents in early life, which may correlate with the temperamental outcome of their present status. Also, 56% of had experienced school bullying, and most participants had hints of one or more psychiatric diseases |
| A 12-month study of the hikikomori syndrome of social withdrawal: Clinical characterization and different subtypes proposal [20] | 2018 | Cohort | Spain | N = 190 | Six major diagnostic groups: affective, anxiety, psychotic, drug use, personality and other Axis I disorders. Only one case corresponded to primary hikikomori. Social isolation was more frequent in men. The anxiety-affective group had lower clinical severity but worse evolution. Subjects undergoing intensive treatment had a higher medical follow up rate and better social networks at 12 months. |
| Identification of the hikikomori syndrome of social withdrawal: psychosocial features and treatment preferences in four countries [23] | 2015 | Cross national case series | India, Japan, Korea, USA | N = 36 | Participants had high levels of loneliness (UCLA Loneliness Scale M = 55.4, SD = 10.5), limited social networks (LSNS-6 M = 9.7, SD = 5.5) and moderate functional impairment (SDS M = 16.5, SD = 7.9). Of them 28 (78%) desired treatment for their social withdrawal, with a significantly higher preference for psychotherapy over pharmacotherapy, in-person over telepsychiatry treatment and mental health specialists over primary care providers. |
| Hikikomori: The Japanese Cabinet Office’s 2016 Survey of Acute Social Withdrawal [29] | 2017 | Survey | Japan | N = 5000 | It estimated 541,000 cases of hikikomori, with prevalence population of 1.6%. 60% males, half between 20 to 29 years old, 70% unemployed |
| Lifetime prevalence, psychiatric comorbidity and demographic correlates of “hikikomori” in a community population in Japan [19] | 2010 | Survey | Japan | N = 4134 | A total of 1.2% had experienced hikikomori in their lifetime. Among them, 54.5% had also experienced a psychiatric (mood, anxiety, impulse control, or substance-related) disorder in their lifetime. Respondents who experienced “hikikomori” had a 6.1 times higher risk of mood disorder. Among respondents, 0.5% currently had at least one child who had experienced “hikikomori”. While psychiatric disorders were often comorbid with “hikikomori”, half of the cases seem to be primary hikikomori without a comorbid psychiatric disorder. |