The hikikomori population varies significantly depending on the definition used: Evidence from a survey in Kasama, Ibaraki, Japan

Recently, the concept of “hikikomori”—people avoiding social participation (such as attending school, working, or socializing outside the home) and generally staying at home for more than 6 months as a result of various factors—has drawn increasing attention, in the fields of both psychiatry and social isolation. In 2015, a study by the Japanese Cabinet Office reported that approximately 1.5% of residents in Japan could be defined as hikikomori. ¹ A more recent survey ² suggested that the population has reached over 1.7 million. This suggests an urgent need for nationwide action to support this group.

There has, however, been little discussion about what characteristics could define hikikomori. Teo and Nonaka claimed that this will stifle the advancement of the field of hikikomori research, and suggested the need to reconsider the rationale underlying existing criteria and the development of a standard definition.^{3, 4, 5} There are two major criteria which are often used, proposed by the Japanese Cabinet Office ¹ and Kato and colleagues.^{6, 7} The former adopted the first definition of hikikomori proposed by Saito, ⁸ while the latter, recently published in journals and used in the psychiatric field, distinguishes between pathological and non‐pathological hikikomori. ⁷ Each criterion has three main items, two of which are common to both and one of which is different (see Table S1). However, few surveys have estimated the prevalence of hikikomori using the Cabinet Office criteria, and no study has considered both. We therefore carried out a survey using both diagnostic criteria. We aimed to determine the actual percentage of the population meeting each criterion and to identify overlaps and differences between the groups defined by each criterion.

We conducted a postal questionnaire survey among the residents of Kasama City in Ibaraki Prefecture, Japan by sending questionnaires related to both definitions to 4000 people (2000 men and 2000 women) stratified by age for each gender. Participants could respond by post or online. The survey period was from February to March 2024. For the weighted tabulation, we also asked about respondents' age and gender. We calculated the number of people who met each definition of hikikomori and categorized them into three types of hikikomori (pathological, non‐pathological, and Cabinet Office's hikikomori) and used weighted tabulation to make an accurate estimate of the number of hikikomori in Kasama City. We excluded incomplete answers. This research was conducted in accordance with the Declaration of Helsinki and approved by the Medical Ethics Committee, University of Tsukuba (Approval No. 1950‐1) and it conforms to the provisions of the Declaration of Helsinki. We respected the participants' right to privacy obtained informed consent from all participants.

We obtained 1137 valid responses, resulting in a response rate of 28.4%. Among the 57 individuals classified as pathological hikikomori, 21 were also classified as Cabinet Office's hikikomori. Additionally, among the 201 individuals classified as non‐pathological hikikomori, 59 were found to meet the Cabinet Office's hikikomori. Cabinet Office's hikikomori was included within either pathological hikikomori or non‐pathological hikikomori. The detailed results are illustrated in Fig. 1a,b. The weighted tabulation suggests that 8972 people in Kasama City meet the non‐pathological hikikomori and 5096 people the pathological hikikomori and 4239 people the Cabinet Office's hikikomori.

Fig. 1.

Venn diagrams of respondents who meet each definition of hikikomori. The percentages in brackets are (1) percentage of total respondents, and (2) percentage of respondents included in this set. (a) Relationship between pathological hikikomori group and Cabinet Office definition group (n = 116). (b) Relationship between pathological hikikomori group and Cabinet Office definition group (n = 222).

Our findings indicate that while both pathological and non‐pathological hikikomori may include individuals classified as the Cabinet Office's hikikomori, many cases of pathological hikikomori do not align with the Cabinet Office's hikikomori, and the majority of non‐pathological hikikomori also do not align with it. We argue that although both definitions and criteria are valuable, misinterpretations of hikikomori may persist if the differences in definitions and population characteristics are not clearly understood. Furthermore, upon reviewing the surveys conducted by Municipalities,^{9, 10} the definition and criteria set forth by the Cabinet Office have not been strictly adhered to in many cases. Therefore, caution must be exercised when interpreting and comparing the results.

Kato ⁶ pointed out that the Cabinet Office's definition sees hikikomori as a non‐psychotic phenomenon. When considering psychiatric interventions or surveys that focus on the need for support for this group, including medical treatment, it is essential that the appropriate criteria are chosen to fit the situation. It is crucially important to recognize that hikikomori is not a diagnosis but a condition. Medical intervention may be necessary to address secondary disorders and differentiate mental states, including developmental disorders, that may arise if the condition becomes prolonged. ⁷ We believe it is essential to reconsider the purpose of creating criteria and to continuously discuss their validity to genuinely support the parties involved. It is also important to reaffirm the importance of not over‐medicalizing hikikomori, while also correctly assessing and responding appropriately to psychiatric symptoms.

Funding information

This work was supported by JST RISTEX “SOLVE for SDGs: Preventing Social Isolation & Loneliness and Creating Diversified Social Networks” Grant Number JPMJRX21K2, Japan.

Disclosure statement

Kaoru Tamura, Takafumi Ogawa, Yuki Shiratori, Haruhiko Midorikawa, Miyuki Aiba, Daichi Sugawara, Tamaki Saito, Chie Yaguchi, Takafumi Hori, Hirokazu Tachikawa declare no relevant conflicts of interest.

Supporting information

Table S1. Differences between the Cabinet Office's definition of hikikomori and Kato's definition of pathological social withdrawal. The common items (1 and 2) are underlined and the items that are different (3) are highlighted.