Our results show that IED diagnosis in Korea has been increasing since 2002. It showed an even steeper increase in the last decade, especially since 2012. As the number of IED diagnoses as primary diagnosis keeps increasing, more attention should be given, and preventative measures should be taken to avoid the onset at an early stage. Also, the possibility of the underrated number of IED should also be considered. Japan's research may explain the overall low prevalence of IED in South Korea compared to the U.S. and other countries. Yoshimasu et al(2011) revealed that the low prevalence of IED in Japan compared to U.S. studies can be attributed to cross-cultural factors. They reported that Japanese tend to suppress their feelings, especially anger, compared to westerners, due to social norms. This might also be true for South Koreans since collective actions are valued rather than individual or personal opinions. In this social context, showing one's feelings, especially anger, will isolate an individual from other society members. The result also showed that ADHD as a most frequent comorbid disease with IED in Korea. ADHD symptoms are quite different from depression, by which we can infer that the IED vulnerable population in Korea might have different characteristics compared with other countries.
Our findings also reveal that the gender gap in IED diagnosis is increasing and that IED might be a gender-specific disease. The number of diagnoses is higher in men and continues to increase. Although epidemiological evidence is limited, gender difference in IED has also been reported in previous literature. A study in United States also found that IED was about twice as frequent in men than in women [8, 9]. In general, gender disparities are among the most vital indicators of mental health problems [10]. Men and women experience substantially different emotional problems [11–12]. Whereas women experience internalizing feelings, turning problems against the self into depression and anxiety, resulting in more attributions of self-blame and self-reproach [13–15], in contrast, men show higher prevalence of externalizing disorders than women, including antisocial personality disorders and substance abuse or dependence [16–17].
IED prevalence was prevalent in the age group 20–29 years, which is consistent with previous finding tht IED prevalence higher in young individuals under 35 years old [4, 18, 19] than other older age groups. Researchers have speculated that high rates of depression in early adulthood can be attributed to a relative lack of experience in coping with life transitions that occur at that time. In contrast, middle age is associated with greater maturity [10, 20–22]. In this perspective, a high prevalence in the age group 20–29 years may be attributed to the immature and inexperienced self of age group 20–29 years in controlling their feelings.
The gap between the diagnosed and those who seek medical help, especially outpatient visits, was also identified. Whereas men are more likely to be diagnosed than women, women seek more professional help, visiting hospitals frequently than men. Although not IED specific, previous research has reported that women recognize psychological problems more often than men and are more likely to seek treatment for psychological problems or psychiatric disorders [23–26]. Also, women visit psychiatric departments more frequently than men [24, 27–29]. Also, while residing around capital area was not statistically significant in the diagnosis, residence in capital city was significantly related to more individual medical spending. Although further investigation is needed, less medical spending can be attributed to lack of accessible hospitals, considering that issues of hospital deficit in rural areas have been around for several years. The fact that discrepancy between the diagnosed population and people seeking medical help exists should be highlighted, implying that population with high vulnerability is not getting appropriate care. Also, because currently no study can provide information on whether people voluntarily sought medical care or not, more attention should be given to IEDs to identify vulnerable population in need of care, and facilitate early detection, preventing further social burden it can bring about.
Several limitations should be considered interpreting the findings. First, the NHIS data represents medical records rather than a survey. Only nominal reports such as changes in IED diagnosis and their medical service use were available based on the limited variables available. Second, the NHIS data only captures those who visited the medical institution. Therefore, IED patient characteristic before the entry of medical institution could not be determined. Despite these limitations, this study sheds light on IED, an often-neglected disease in South Korea. While aggressive behaviors and failure to control individual’s anger can lead to physical and social adverse outcomes, much of previous studies dealing with mental disorders are focused on depression, schizophrenia, or bipolar disorder. In his study, Coccaro also suggested that IED often precedes the aforementioned diseases and should be examined independently rather than as a comorbid disease [4].
NHIS encompasses over 97% of the Korean’s medical records, a reliable source as a representation for the national population, despite limitation of variables due to its originality as a medical record rather than a survey. This study has value in that it represents preliminary data for further IED research within a nationally representative data. In addition, the records are largely exact, based on physician’s professional diagnosis, not on self-administered responses. Finally, since IED is classified as an acute disease, these data are not open to the public and can only be obtained in claims data.