Materials and methods
A questionnaire was administered to university students (N = 203) from six universities in the metropolitan area of Japan, and the responses of participants without missing data were analyzed (N = 202). Many of them were undergraduates, but some were graduate students. The participants included 54 men, 146 women, and two respondents who did not disclose their gender. Their age ranged from 18 to 28 years, with a mean age of 20.09 years (SD = 1.78).
Japanese version of the External and Internal Shame Scale (EISS-J)
The EISS contains eight items rated on a 5-point Likert scale ranging from 0 to 4, with four items assessing external shame and four assessing internal shame. The original EISS contained the following core domains of shame experiences: (1) inferiority/inadequacy, (2) sense of isolation/exclusion, (3) uselessness/emptiness, and (4) criticism/judgment, resulting in a pool of 16 initial items. Subsequently, researchers selected one pair of items from the pool that adequately expressed each domain. Consequently, a scale consisting of final eight items was developed (example items in the inferiority/inadequacy domain included “I am different and inferior to others” and “People around me see me as not being up to their standards”) . The English version was translated into Japanese by two experts (YH and YK) after obtaining the original authors’ approval. Back-translations were conducted by two native English speakers from a translation company (Crimson Interactive Japan Co., Ltd.). The two retranslated English versions were integrated, and the resulting version was sent to the original author, who confirmed the homogeneity of the Japanese version of the scale.
Japanese version of the Other as Shamer Scale (OAS)
The OAS was developed to assess external shame . The Japanese version is composed of 18 items rated on a 5-point Likert scale ranging from 0 to 4, which are similar to the original version . A strong positive correlation was reported between the EISS and the OAS .
Japanese version of the State-Trait Anger Expression Inventory (STAXI)
The STAXI was developed to measure anger . The Japanese version, which contains ten items of the Trait Anger scale rated on a 4-point Likert scale ranging from 1 to 3, was used in the present study . A positive correlation between anger and external shame was confirmed . A total of 106 participants responded to the STAXI, as the STAXI was added midway through the study to reinforce the examination of the validity of external shame.
Japanese version of the Fear of Compassion Scale (FC)
The FC  and its Japanese version  are composed of three subscales that include 38 items: fear of compassion for others (FCforO, ten items), from others (FCfromO, 13 items), and for self (FCforS, 15 items). This scale is rated on a 5-point Likert scale ranging from 0 to 4. Fear of compassion is the sense of resistance to expressing compassion for others or receiving compassion from others. Previous research noted shame memories as a background to the fear of compassion, suggesting that shame experiences increase depression and anxiety, mediated by fear of compassion for and from others .
The Japanese version of the Beck Depression Inventory-Second Edition (BDI-II)
The BDI-II  and its Japanese version  assess depression. The high validity and reliability of the scale for assessing depression have been confirmed . The scale contains 21 items rated on a 4-point Likert scale ranging from 0 to 3.
Japanese version of the Humiliation Inventory (HI-J)
Humiliation, like shame, is a form of self-consciousness emotion . It has been shown that during the experience of shame, there is an aggressive aspect that is focused on others. . A positive correlation was predicted between the HI-J and the EISS-J by using the 12 items of cumulative humiliation rated on a 5-point Likert scale ranging from 1 to 5.
Japanese version of the Depression, Anxiety, Stress Scale-15 (DASS-15)
The DASS-15 consists of 15 items rated on a 4-point Likert scale ranging from 0 to 3  and is used to assess depression, anxiety, and stress. A positive correlation was demonstrated between the DASS-21 and the EISS . Therefore, the present study predicted a positive correlation between the DASS-15 and the EISS-J.
An online questionnaire was conducted with university students enrolled in six Japanese universities that agreed to participate in the research. Participants were recruited by providing a link to the survey to students attending online lectures and one university also on the universities’ subject recruitment websites. The survey was conducted between July and November 2020. Responses were anonymous. Participants were provided with written explanations regarding the survey’s purpose, personal information protection, confidentiality, and arbitrariness of responses. Afterwards, participants were instructed, “If you agree to complete the survey after reviewing the above instructions, please click the ‘Answer’ button below to proceed and answer the questions. This study was approved by the ethics committee of Chiba University (No. 3441). The number of accesses to the site was 577, and the number of respondents was 203 (35.18%). However, test accesses and multiple accesses by the same person are included. Emails were sent to the participants three weeks after the survey, requesting them to participate in the online retest study to identify the scale’s test-retest reliability. The emails contained the URL of the retest questionnaire. Participants were able to respond on the same day or later. All respondents completed the survey within five weeks of the initial survey, except for one who completed it eight weeks after the initial survey. The method for obtaining informed consent was the same as that in Study 1. Statistical analyses were conducted using SPSS and AMOS software.
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