South Korea has adopted a mandatory military service system. Therefore, unless there is a special reason for exemption, all Korean men over the age of 18 years are duty-bound to enroll in military service. Military service is an important issue affecting an individual’s life and the nation as a whole. It is no exaggeration to say that military duty is one of the most predominant influence on the life of Korean men in their 20s. Challenging environments with limited autonomy and the separation from previous social support systems can lead to various problems with adaptation [1-3]. As the grievances and social impact of men in relation to the military service are high, it is important to understand the psychological characteristics and mental health of young people who are expected to have difficulty in adapting to the military service, and provide directions for intervention.

According to the Military Manpower Administration (MMA) report in 2017, about 93% (n=101,759) of enlisted people aged between 20 and 22 years are enrolling themselves for military service [4]. The early 20s is the beginning of adulthood, marked by a period of confusion and instability. In addition, early adulthood is a biologically vulnerable period for onset of major mental disorders [5,6]. However, unlike other physical illnesses, mental illness is likely to be discovered just before joining the military or immediately after enrollment, due to its implicit nature. About 42.5% of disqualifications of people through military screening tests performed by the MMA were found to be due to neuropsychiatric problems in 2017. About 55.2% returned home after joining the military due to psychiatric problems, and this proportion is increasing annually [4].

Military service itself can act as a significant stressor. Especially, the young generation is habituated to individualism and has a relatively high level of education and rich living conditions; often, their personal values are likely to conflict with military values represented by a hierarchical structure [2,7]. As a result, as young Korean men are under substantial pressure about military service, their animosity regarding the issue is increasing. This is particularly true for those who experience uncertainty regarding military life before joining service, based on others’ negative experiences with the military, media reports, own fear of disconnection from society, worries about future plans, and environmental changes [2,7,8].

According to the stress-vulnerability model, the interaction of biologically predisposed vulnerability and environmental stress can cause the onset and the exacerbation of various mental disorders [9]. Therefore, a systematic evaluation and multifaceted understanding of mental health of young men prior to their military enlistment is essential. Previous studies, however, focus primarily on soldiers in the military service, in trying to preventing extreme behaviors such as suicide, gunshot accidents, and desertion from the army [1,3,10-14]. However, there is little research on mental health and psychological features of young men prior to their enrolment in military service, and psychiatric evaluation for them tends to be used only as a tool for screening, rather than understanding and improving their individual lives.

This study included young men who were referred for psychiatric evaluation because they had or were expected to have difficulty in adapting to military life for some psychiatric reasons. The present study used Latent Profile Analysis (LPA) to organize respondents into subgroups with similar psychiatric symptoms and personality patterns based on profiles of Minnesota Multiphasic Personality Inventory-2 (MMPI-2) and Temperament and Character Inventory (TCI). LPA is a classification method that estimates latent classes (i.e., subgroups with distinctive features) of participants based on their responses on continuous variables [15]. LPA is one of the person-centered statistical approaches that is different from the variable-centered approach. Variable-centered analyses with more than three interacting variables are difficult to interpret and may be less suitable for making inferences about individuals because the results are at the level of the variable, not the person. On the other hand, person-centered approach enables inferences regarding the distinctive nature of individuals based on shared characteristics of multiple variables within homogeneous subtypes. We used the MMPI-2 and TCI, which are the most widely used psychological assessment for personality and psychopathology as the predicting variables for latent profile analysis. The MMPI-2 and TCI are multiscale inventories and not only the elevation of a single scale but also the overall configuration and interaction of scales are important factors in predicting personality, behaviors and mental health characteristics. Both inventories were therefore considered suitable for LPA [16,17].

This study aimed to provide an in-depth understanding of young men referred for a psychiatric evaluation for military service-related adaptation issues and promote development of clinical intervention strategies by integrating characteristics including demographic, psychiatric symptom, temperament, and personality.

This study examined the sociodemographic, clinical, and psychological characteristics of Korean young men who were referred for a psychiatric evaluation due to anticipated military maladjustment and identified their subtypes based on the profiles of MMPI-2 and TCI. About 30-40% of participants had a psychiatric history (n=152) and familial loading of mental disorder (n=98). About 30% of them experienced parents’ divorce (n=102) and exposure to direct or indirect domestic violence (n=115). About 55% (n=192) of the sample were unemployed without studying or working. Approximately 70% reported clinically significant level of depression and state and trait anxiety. In addition, 52.4% (n=206) reported suicidal ideation at a clinical level, with about 26% (n=90) classified as severe in this regard. These findings suggest that they were likely to be in socially or psychologically vulnerable situations.

In the next step, we conducted LPA to investigate subgroups of the participants based on their MMPI-2 and TCI profiles. By using MMPI-2 and TCI together as indicators in LPA, we attempted to identify heterogeneity of the participants considering various psychiatric symptoms, biological temperament, and underlying personality structure. The LPA identified four classes with distinctive psychological features: Class 1 (nonclinical: n=68, 19.5%), Class 2 (internalized: n=129, 37%), Class 3 (externalized: n=60, 26.1%), Class 4 (confused: n=91, 26.1%). Class 1 did not complain distinct clinical symptoms and had a relatively adaptive and stable temperament and personality structure. Class 2 showed a relatively higher level of harm avoidance in TCI and 2-7 code type in MMPI-2. These individuals tend to have inhibited, shy, timid, and self-critical characteristics and so are likely to be vulnerable to internalizing disorders such as depression and anxiety. Individuals with code type 2-7 are known to be highly motivated for treatment because they experience high subjective distress and seek help [21]. Class 3 and Class 4 shared similar profiles on the MMPI-2. However, Class 3 showed a relatively higher level of novelty seeking and more aggressive and hyperactive tendency than Class 4. Class 3 showed the highest proportion of smoking, drinking, and history of conduct behavior among the four classes. Class 4 showed the most severe level of almost all psychiatric symptoms and diminished sense of reality. Class 4 seemed to be the group with the high risk showing confusing mixture of symptoms with difficult temperament and immature personality strucutre [36].

Classification using a person-centered approach can provide clinically useful criteria that complement the categorical diagnostic systems of mental disorders. In the past decades, limitations of categorical diagnostic systems such as the DSM and International Statistical Classification of Diseases and Related Health Problems (ICD) have been proposed [37,38]. Categorical approaches have some limitations such as high comorbidity of disease, oversimplification of individual attributes, and overlooking the underlying psychological structure of psychiatric symptoms. Moreover, we reviewed the medical chart and attempted to categorize the participant’s diagnosis based on the ICD (Supplementary Table 2 in the online-only Data Supplement), but approximately 39% of participants belonged to two diagnostic categories, and 28% belonged to three or more different diagnostic categories simultaneously, suggesting high comorbidity. Thus, the four-class solution in this study, based on individual multidimensional characteristics, may help overcome the limitations of categorical diagnostic systems and help plan therapeutic interventions for participants by providing comprehensive clinical conceptualizations.

However, the possibility of malingering should be carefully considered to ensure the validity of the four-class solution. In particular, Class 4 scored high on the variables related to the faking-bad tendency. This could be because as many young men should involuntarily perform military service, many are presumably motivated to avoid military service. However, the instruments used in this study seem to have limitations in detecting malingering. The KMDT is a widely used forced-choice test that requires the individual to choose one of two response options, and has a very low difficulty level. As the KMDT was too simple and easy, only two of 348 participants in the study were in the range of “probable malingering.” The F family scales (F, FB, and FP) in MMPI-2 measure infrequent symptoms that are not usually reported by the general population or even by actual psychotic patients [39]. However, the elevation on F family scales do not always indicate that the respondents are trying to lie, because the F scales are known to correlate with mental confusion and psychotic experiences, and faking bad can occur with or without actual symptoms [40]. In general, the extremely high score (inpatients: ≥100T, outpatients: ≥90T) on the F scale suggests that the profile may be invalid [41]. The next range of scores (inpatients: 80-99T, outpatients: 70-89T) suggest that the subjects may exaggerate their symptoms or problems. However, they may exaggerate their symptoms as part of “crying for help.” [39,41] Class 4 showed mean score of 75T on F scale, which implies that Class 4 might consist of those who really had serious psychiatric symptoms and are crying for help or those who reported more severity of symptoms than the actual level. Therefore, further research and discussion are needed for effective instruments to detect of malingering on mental tests [42].

Another main finding of this study is about intellectual ability of overall participants. There were no statistically significant differences in IQ indices among the four classes although Class 4 tended to score the lowest. However, the mean IQ of total participants (M=91.3, SD=17.6) was about nine points lower than the mean of the general population (M=100, SD=15), and especially the processing speed index was about 15 points lower (M=85.9, SD=16.6). This study excluded those who had general communication difficulty or were clearly diagnosed with intellectual disability. Therefore, the participants in this study may include people with lower intelligence which was not detected so far, or whose IQ was not low enough to be diagnosed as intellectual disability. About 16% (n=55) participants belonged to a borderline intelligence range (generally IQ 70-79), about three times more than the proportion of 6.7% in the general population. Of course, IQ, especially processing speed can be reduced by psychiatric symptoms such as psychomotor retardation and performance anxiety or underestimated due to low level of motivation. However, even for Class 1, who did not report significant clinical symptoms, the Verbal Comprehension Index (M=98.3, SD=16.2), Perceptual Reasoning Index (M=97.5, SD=18.5), and Working Memory Index (M=97.7, SD=18.3) were very close to 100, whereas the mean Processing Speed Index recorded only 88.8 (SD=16.5). This suggests that some participants originally had lower information processing speed regardless of their psychiatric symptoms. Processing speed is a primary element of intelligence and mental capacity. It is also believed to be linked causally to other elements of intelligence and mental functioning [43,44]. Those with slower processing speed may be not adaptive in the face of challenging situations such as military service, when they need to quickly learn new rules and keep pace with others. Slower processing speed is likely to cause problems not only in adaption to military duty but also in their future including seeking employment or long-term daily lives. In order to adapt to the rapidly changing information age, the abilities to quickly select the necessary information from a vast amount of resources and multitask are required. In addition, in the age of highly developed technology, machines or artificial intelligence are replacing the simple tasks that were previously performed by low-skilled workers. Therefore, it is time for the society to seriously consider the adaptation problems of young men with cognitive weakness, such as borderline intellectual functioning or low processing speed, although these are not intellectual disabilities.

Some limitations of this study should be mentioned. First, because a cross-sectional design was employed, we were unable to infer causal relationships between the variables. Longitudinal studies should be conducted to clarify causal relationships and changes over time. Second, the generalizability of our finding is restricted because this study was based on a single center, potentially causing sampling bias. Multi-center studies and replications of the current study are needed to validate primary findings such as the four-class solution and lower processing speed of participants. Third, because sociodemographic data were collected retrospectively through chart reviews, in some cases, the exact information could not be identified. Fourth, structured diagnostic interview tools such as Structured Clinical Interview for the DSM (SCID) were not used in this study. If such tools were included, it would have helped to identify the correspondence of four-class solution and official diagnosis. Fifth, this study did not include objective measurements to assess participants’ daily living adaptability such as interpersonal skills, academic achievement, and occupational ability.

Despite these limitations, the results of the study have the following implications. Although prior to military service, young men often report many psychological problems in stressful situations, few studies have been conducted in this regard. This study has significant implications in that it focused on the mental health and adaptation problems of young men who were expected to have difficulties in military life, and it attempted to identify subgroups through a person-centered approach based on combinations psychiatric symptoms and personality structures. Recognizing heterogeneous subgroups in a sample can benefit clinical conceptualizations and therapeutic intervention [17,45]. Such attempts are not limited to providing criteria for determining military suitability or preventing accidents during military service. Apart from the issue of military service, young adults who lack adaptability may experience significant distress throughout their everyday lives in social and occupational functioning. However, these young adults are no longer the subject of social concern after exemption from military service or the end of their military duty. As they are still in their early 20s when they are exempted from such duty, most of them live under the care of their parents. However, as their parents become older or die and the family system weakens, their lack of adaptability and independence can be a serious social problem. Thus, this study is expected to be the cornerstone of therapeutic interventions and social discourses that will benefit not only their military adaptation, but also their future daily adaptation.