1. Our study shows that the Turkish version of the IED-SQ scale is a valid and reliable measurement tool.

2. Our study represents the initial adaptation of the IED-SQ.

3. Our study revealed that the IED-SQ scale can be used in clinical practices to identify the presence of IED.

Intermittent Explosive Disorder (IED) is an impulse-control disorder characterized by recurrent episodes of failure to resist impulses that result in severe acts of aggression or harm to others’ property [1]. IED was initially described by Esquirol in 1838 as “impulsive monomania”, and referred to as “partial madness” [2]. IED, originally termed “Passive-Aggressive Personality-Aggressive Type” in the Diagnostic and Statistical Manual of Mental Disorders-I (DSM-I), and “Explosive Personality” in the DSM-II, was referred to as IED in the DSM-III and thereafter. In the DSM-5, IED is classified under the category of “Disruptive, Impulse-Control, and Conduct Disorders”, alongside diagnoses like pyromania, kleptomania, and trichotillomania [3].

Although impulsive, aggressive behaviors and anger outbursts are commonly observed in society, the diagnosis of IED is often overlooked in psychiatric clinics. This low incidence of diagnosis frequently stems from shortcomings in the DSM criteria, and it has been argued that a more precise accounting of the prevalence of true IED in the community could be determined by revising the criteria. Coccaro developed “Research Criteria” (IED-RC) in an attempt to rectify the situation [4, 5]. Coccaro et al. [6] determined that the use of the IED-RC diagnostic criteria produced a highly reliable (0.87) level of diagnosis of lifelong IED. Cases diagnosed using IED-RC displayed higher levels of aggression, impulsivity, and impairment in functioning than did those diagnosed with Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision (DSM-IV-TR) diagnostic criteria [4, 6]. The changes in the DSM-5 were primarily based on IED-RC [4].

IED patients struggle to restrain impulses that lead to verbal or physical outbursts. IED patients’ aggressive behaviors are often impulsive and disproportionate to provocation. Individuals with IED may experience intense distress, psychosocial impairment, and self-harm tendencies [7]. Individuals with IED frequently exhibit comorbid psychiatric disorders. Although the comorbidity of Attention-Deficit/Hyperactivity Disorder (ADHD) and IED has not been extensively examined in previous studies, it is not surprising to see them co-occurring, given that both disorders involve issues with impulse control [3, 8].

Hypotheses regarding the etiology of impulsive aggression and IED can be categorized into two main themes. The first involves adverse early childhood experiences that may affect the development of crucial attributes such as self-control, impulse control, deferred gratification, and the ability to cope with frustration, all of which are central to suppressing impulsive aggression. The second theme suggests that impulsive aggression is associated with imbalances in brain function related to behavioral arousal and inhibition; this perspective has gained strength over the past two decades with the support of numerous research findings [9].

Epidemiological studies of IED suggest that this diagnosis may be more common than previously thought [10, 11, 12]. Felthous et al. [13] diagnosed 3.4% of 443 male volunteers with complaints of violence and aggression as IED. Coccaro et al. [14] identified a lifetime prevalence of 3.95% for IED among 253 individuals in Baltimore, but when the same sample was evaluated using Intermittent Explosive Disorder - Research Criteria (IED-RC), the prevalence increased to 5.14%. Gelegen and Tamam found the lifetime and annual prevalence rates of IED in 406 patients seeking outpatient services for the first time to be 16.7% and 11.3%, respectively, according to DSM-5 criteria [5].

IED can potentially lead to significant public health issues, as it is a treatable, widespread behavioral disorder. Individuals with IED may not actively seek treatment, so recognizing this diagnosis is of paramount importance. Moreover, the need for a scale that can facilitate diagnosis is evident [5, 15]. Intermittent Explosive Disorder Screening Questionnaire (IED-SQ) is considered a potentially valuable screening tool for identifying the presence of IED in adults [16]. The present study was designed to assess the validity and reliability of a Turkish adaptation of the IED-SQ that was developed by Coccaro.

We found that IED is more frequently diagnosed in men, young people, and individuals living in city centers rather than small towns. No association was found between IED and gender, marital status, educational level, or socioeconomic status (Table 1).

BPAQ, BIS-11, and SCL-90-R total scores and subscale averages were higher in the patient group than in the control group (Table 2). There was a significant relationship between the groups and the WURS score, with more individuals testing positive in the patient group than in the control group. According to the MIDI-IED scale, no IED individuals were in the control group, whereas 84.5% of the patient group tested positive for IED. Using the IED-SQ, 87.3% of the patient group tested positive, with no positive individuals in the control group.

Based on the Hosmer-Lemeshow test, the model fits well (p = 0.83), with Nagelkerke R-Squared at 0.81 and Cox & Snell R-Squared at 0.60. The independent variables accounted for 81% of variance in the IED-SQ variable (Table 3).

The subscales of the BPAQ, including physical aggression, verbal aggression, hostility, and anger, along with the attention impulsivity, motor impulsivity, and non-planning subscales of the BIS-11, and the variables age, marital status, and place of residence were incorporated into the multivariate analysis to identify factors independently associated with the IED-SQ. The analysis only revealed that the physical and verbal aggression subscales of the BPAQ and the attention subscale of the BIS-11 were independently associated with IED-SQ (Tables 4,5).

A backward-stepwise model was used and the last step (step 5) is shown in Table 5. The Omnibus test for this model had a p-value of 0.001.

Our study revealed that the Cronbach’s $\alpha$ values for the scales were as follows: 0.95 for WURS; 0.95 for BPAQ; 0.91 for BIS-11; 0.98 for SCL-90-R; 0.93 for MIDI; and 0.74 for IED-SQ.

The investigation of human aggression has been hindered for years by the need for more reliable and valid diagnostic criteria for individuals exhibiting impulsive aggressive behavior. IED, which belongs to this behavioral category, needs more and better psychometric measures [11]. Our study’s most significant outcome was the demonstration of the validity and reliability of the Turkish version of IED-SQ. It was observed in the original study by Coccaro that the IED-SQ demonstrated high specificity (90.5%) but low sensitivity (61.0%) [16]. However, our study found a specificity of 100% and a sensitivity of 87.3%, with only 12% of the patient group being overlooked. This may be attributed to including LHA in the DSM-5 diagnostic criteria, which requires more criteria to be met. The combined sensitivity and specificity percentages exceeding 170 suggest that the tests are clinically sound, thus supporting the validity of the IED-SQ as a screening tool [29].

In the original study by Coccaro et al. [16], the internal consistency coefficient of the IED-SQ was 0.80. Barra et al. [30] found that the IED-SQ internal consistency coefficient was 0.79 in 161 young adults; Gharibpour and Akbari [31] found an $\alpha$ of 0.85 in 54 prisoners; and Sheikhi Gerakoui [17] found it to be 0.72 in 665 10th-grade students. In the present study, the Cronbach’s $\alpha$ coefficient of the Turkish version of IED-SQ was 0.74, indicating that the internal consistency was adequate [32].

Previous studies have shown that IED is more common in men than in women [6, 33, 34]. We also observed a 2.5 times higher incidence in men compared with women. Contrary to a previous study in our country, we found that most IED patients (54.9%) reside in city centers [5]. It is worth considering if urban living conditions trigger impulsivity and aggression. Studies have shown that unemployment is a risk factor for IED [5, 35]. In our study, the higher rate of unemployment in the patient group compared with the control group supports this finding. Our study found no relationship between marital status, education level, or socioeconomic status and the patient or control groups. The disease is more prevalent in younger individuals (35–40 years), as consistent with previous studies [15, 34].

Our study showed that significant differences exist in the IED-SQ scores of the patient and control groups in the BPAQ, BIS-11, and SCL-90-R total and subscale scores, as well as in the WURS and MIDI results. These findings are consistent with those reported in existing literature, and support previous studies by Coccaro, Sheikhi Gerakoui, and Kulper, et al. [17, 19, 31, 36, 37, 38], indicating that individuals diagnosed with IED exhibit higher levels of psychopathology, aggression, and impulsivity.

In reviewing the current literature, we observed that individuals diagnosed with IED are likely to experience depression and anxiety symptoms at least four times more frequently than the general population, which is consistent with data from studies conducted by Kessler et al. [11] and from other similar community-based investigations [39, 40]. In the present study, consistent with these findings, individuals diagnosed with IED were found to have 2.5 to 3 times higher rates of depressive and anxiety symptoms than those without the diagnosis. In our study, anxiety and depression were evaluated not as diseases but as symptoms, aiming to avoid confounded effects. However, from another perspective, this approach can also be considered a limitation.

McElroy et al. [33] found that obsessive-compulsive symptoms were reported in 22% of individuals with IED. Our results, in line with current literature, showed that 22.5% of patients diagnosed with IED, based on the IED-SQ, reported symptoms of obsession and compulsion. Additionally, ADHD is considerably more prevalent in IED patients (20%) than in the general population [5, 41, 42]. In our study, supporting other studies, approximately 90% of the patient group diagnosed with IED, according to the IED-SQ, exhibited symptoms similar to ADHD as indicated by the WURS results.

In both previous studies and in our own study, the absence of investigation into the relationship between types of obsessive-compulsive symptoms and types of ADHD underscores the necessity for research in this area.

When the results of the logistic regression analysis were evaluated, the variables contributing significantly to the model were the physical and verbal aggression subscales and the attention subscale. A literature review showed that the IED-SQ, BPAQ, and BIS-11, and their subscales, have been studied together in most studies, and almost all of them showed a high correlation with IED, as we found in our study. The frequent occurrence of anger and impulsivity in patients with IED may have contributed to this result [5, 16, 43].

Among individuals classified as IED patients according to the Turkish version of the IED-SQ, 85.5% were also classified as IED patients according to the MIDI-IED, whereas among those classified as healthy, according to IED-SQ, 90.9% were classified as non-IED according to the MIDI-IED. Our results demonstrated that the IED-SQ has appropriate equivalent validity. The absence of equivalent validity studies for the IED-SQ in the literature suggests that our study could guide future research.

One of the strengths of the present study is that it is one of the few focusing on DSM-5 criteria-based IED in Turkey and is the first study to apply the IED-SQ to a Turkish sample. Participants’ diagnoses were standardized and conducted through structured clinical interviews by a single researcher. To the best of our knowledge, this is the only study investigating the validity and reliability of the IED-SQ in a language other than English.

One of the limitations of our study is the cross-sectional design, which weakens our ability to establish causality. Other limitations are the predominantly self-reporting nature of the scales used, the reliance on entirely self-reported socioeconomic status of participants and their families, psychiatric histories, and the acceptance of obsessions and compulsions, anxiety, and depression as symptoms rather than illnesses. Additionally, the study lacks retest measurements and did not involve inter-rater reliability assessments. Future studies that (a) consider depression and anxiety, which we treated as symptoms, as comorbid conditions; (b) involve larger sample sizes; and (c) include re-test and inter-rater reliability measurements, may help to obtain more comprehensive results.

Our study shows that the Turkish version of the IED-SQ scale is a valid and reliable measurement tool with adequate internal consistency, convergent validity, and equivalent validity. As far as we know, this study represents the first attempt to adapt the IED-SQ to another language. We believe that the Turkish version of the IED-SQ will help to identify Turkish-speaking IED patients more quickly.

The data presenting in this study are available on request from the corresponding author.

Conception–SÇD, CY; Design–SÇD; Supervision–LT, MED; Fundings–SÇD; Materials–CY; Data Collection and/or Processing–SÇD; Analysis and/or Interpretation–LT, MED; Literature Review–CY; Writing–SÇD; Critical Review–SÇD, LT, MED, CY. All authors read and approved the final manuscript. All authors have participated sufficiently in the work and agreed to be accountable for all aspects of the work.

Ethical approval for our study was obtained from the Non-Interventional Clinical Research Ethics Committee of Çukurova University Faculty of Medicine on March 5, 2021 (decision number 33). The study was conducted in accordance with the Declaration of Helsinki. Participants were informed about the process during the interviews, and written informed consent was obtained.

This research received no external funding.

The authors declare no conflict of interest.