Mood instability (MI), generally defined as experiencing “rapid oscillations of intense affect, with a difficulty in regulating these oscillations or their behavioral consequences,” is common and known to be associated with various psychiatric illnesses [1,2]. MI has been demonstrated to be associated with mood disorders and is an important risk factor and precursor for both depressive and bipolar disorders [3,4]. MI is also associated with prominent features of psychosis and can be used to predict the later emergence of paranoid ideation and auditory hallucinations [5]. Additionally, although MI is not included as a diagnostic criterion for attention-deficit hyperactivity disorder (ADHD) in the Diagnostic and Statistical Manual of Mental Disorders (5th edition), research suggests that MI and ADHD symptoms may be linked, with overlapping cognitive and neural correlates [6]. Overall, MI is a clinically significant trait that occurs commonly in various mental illnesses and is associated with poor long-term clinical and functional outcomes [7,8]. In addition to showing associations with the illness course, treatment, and prognosis of psychiatric disorders, MI is also known to be associated with cognitive and social outcomes. As one’s mood influences all cognitive functions [9], MI can impact an individual’s academic performance [10], occupational functioning [8], and social skills [8,11].

As shown by its definition, MI encompasses various features such as frequency and rapidity of mood shifts, intensity of affect, ability to regulate, and reactivity to the environment [1]. Although the importance of MI in both general and clinical settings has been recognized, there is a lack of comprehensive assessments to measure all aspects of MI [1]. In this context, the Mood Instability Questionnaire-Trait (MIQ-T) was developed by Yoon et al. [12]. Briefly, the MIQ-T is a 59-item self-report questionnaire that assesses the trait of MI using the five factors of Lability, Upward Tendency, Downward Tendency, Childhood Instability, and Seasonality. The Lability factor includes items regarding an individual’s overall shifts in affect, energy, cognition, and interpersonal behavior. The Upward Tendency factor measures an individual’s tendency to feel euphoric, excited, and energized, while the Downward Tendency factor focuses on the proneness of an individual to experience negative and unstable emotions such as depression, anxiety, and irritability. The Childhood Instability factor includes retrospective items about one’s mood during childhood, whereas the Seasonality factor evaluates how strongly the seasonal changes affect an individual’s mood, energy, and behavior. The original MIQ-T has demonstrated good internal consistency and construct validity, showing correlations with previously validated scales and questionnaires that aligned with the authors’ expectations. Concurrent validity was established using temperament and personality scales that include the concept of MI, such as the Personality Assessment Inventory-Borderline Features Scale (PAI-BOR). Moreover, significant differences in mean MIQ-T scores among the comparison group and patient groups (major depressive disorder, bipolar I disorder, and bipolar II disorder) were observed, showing promise for the use of MIQ-T in aiding the differential diagnosis of mood disorders and informing clinical decisions regarding medication use and treatment course.

The present study had two goals. First, we sought to develop a short form of the MIQ-T (MIQ-T-SF) that included all five original factors and to examine its reliability and validity. The development of the MIQ-T-SF is warranted, as the original MIQ-T questionnaire has a total of 59 items, which results in a long administration time, reducing the approachability of the measure. Although two versions of a short form were created as part of the original MIQ-T development study that was conducted in a clinical sample of patients with mood disorders [12], these short forms did not include the Seasonality factor as the statistical processes at the time prioritized items with the highest loadings on the exploratory factor analysis (EFA). However, as seasonal changes in mood and behavior can be seen in both the general population [13,14] and in psychiatric patients without a diagnosis of seasonal affective disorder [15,16], seasonality appears to be an important dimension within MI and, thus, should be included in the short form. Second, we aimed to compare the MIQ-T-SF scores with regard to gender and age groups in the general population, to better understand its utility and applicability. While the original development of the MIQ-T was focused more on its application in psychiatric settings, the MIQ-T-SF is aimed to be utilized in various other settings such as schools or medical primary care to evaluate one’s trait of MI and provide appropriate resources. Therefore, the usefulness of the MIQ-T-SF should be validated in the general population to clarify the fundamental impact of MI on people’s thoughts and behaviors.

The present study developed a MIQ-T-SF that demonstrated the same factorial structure as the original MIQ-T and evaluated its reliability and validity. The EFA conducted via principal component analysis using direct oblimin rotation resulted in a 17-item MIQ-T-SF and found a five-factor structure, which is the same as that of the MIQ-T. The CFA results confirmed this five-factor structure. Importantly, the MIQ-T-SF also demonstrated great internal consistency for each factor and the complete questionnaire via Cronbach’s alpha and Mcdonald’s omega coefficients. As expected, the five factors demonstrated significant positive correlations with each other, the most pronounced being between Lability and Downward Tendency. However, as these correlations were moderate at most (i.e., r<0.7), we can conclude that these factors are independent but related features of the MI trait. In addition, correlations between the corresponding factors and the total scores of MIQ-T-SF and MIQ-T were found to be excellent, supporting the construct validity of the short form. Overall, these findings demonstrate that the MIQ-T-SF is a reliable and valid scale that encompasses and assesses the various features of MI.

All original factors of the MIQ-T were maintained in the MIQ-T-SF. The MIQ-T-SF is a 17-item self-report questionnaire with five factors: Lability (five items), Downward Tendency (three items), Upward Tendency (three items), Childhood Instability (three items), and Seasonality (three items). The five-factor structure of the MIQ-T-SF mirrors that of the MIQ-T and is consistent with previous literature [1,2,12]. Although the original MIQ-T was developed in a clinical psychiatric population, the MIQ-T-SF still proved to be a good fit for the data in the general population as shown via a CFA. Apart from the chi-square test (which is easily influenced by sample size), all goodness-of-fit indices demonstrated that the five-factor structure was acceptable. Regarding reliability, the MIQ-T-SF demonstrated high internal consistency values for each factor and the complete questionnaire. All five factors of the MIQ-T-SF were positively correlated with each other. However, since these correlations did not exceed a threshold of 0.7, which is the criterion for a strong correlation [23], the five factors can be regarded as independent yet interrelated dimensions within a single trait of MI.

The construct validity of the MIQ-T-SF was examined via correlation analyses using the original MIQ-T scores and other clinically relevant scales. All factors of the MIQ-T-SF showed strong, positive correlations with the corresponding factors of the MIQ-T, indicating a stable factorial structure and conceptual unity with the MIQ-T. In addition, the total MIQ-T-SF score exhibited excellent positive correlation with the total MIQ-T score, demonstrating that the MIQ-T-SF is a valid and effective alternative to the MIQ-T. Correlations between the MIQ-T-SF and other clinically relevant scales generally mirrored correlations observed when using the full MIQ-T. Compared to the TEMPS-A, which includes several temperamental types as subscales, we expected moderate to strong, positive correlations with all temperaments, except for the hyperthymic scale, as that was the case for the full MIQ-T. In addition, the cyclothymic, depressive, irritable, and anxious scales in the TEMPS-A represent negative affect and instability in mood, energy, and behavior, which is characteristically similar to the trait of MI. Thus, we expected the MIQ-T-SF to correlate with these subscales, and the results were consistent with our expectations. The MIQ-T-SF demonstrated moderate to strong, positive correlations with the cyclothymic, depressive, irritable, and anxious subscales in TEMPS-A while showing a weak, negative correlation with the hyperthymic subscale. Concurrent validity was also evaluated using PAIBOR, a scale within the PAI that assesses borderline personality symptoms. The characteristic symptoms of borderline personality disorder include mood lability, identity problems, and unstable interpersonal relationships, which are also associated with MI. Thus, the MIQ-T-SF total score demonstrated a moderate, positive correlation with the PAI-BOR total score. Among the PAI-BOR subscales, Affective Instability, which includes items similar to the Lability factor in the MIQ-T-SF, showed the strongest correlation with the MIQ-T-SF total score. Other MIQ-T-SF and PAI-BOR subscales were also significantly correlated, with the exception of Upward Tendency and Self Harm. Consistent with previous research, MIQ-T-SF scores correlated significantly with measures of temperament types and borderline personality, which are associated with the concept of MI.

In accordance with the second aim, we examined the differences in MIQ-T-SF scores between genders and age groups. Before comparing across groups, we confirmed the measurement and structural invariance of the MIQ-T-SF by conducting a multi-group CFA. All models (configural invariance, metric invariance, and scalar invariance) were deemed acceptable, indicating that the same construct was measured across gender and age groups. The Kruskal-Wallis analysis revealed significant score differences for all factors between genders, except for Childhood Instability: females scored higher than males on Lability, Downward Tendency, Upward Tendency, and Seasonality than did males. This finding is somewhat consistent with previous literature, as many studies have found that females scored higher than males on the dimensions of MI. With respect to TEMPS-A, females usually score higher on the depressive, cyclothymic, irritable, and anxious subscales (i.e., dimensions of negative affect) while males usually score higher on the hyperthymic temperament subscale (i.e., a more positive construct of being full of energy and having an optimistic disposition) [24-26]. Interestingly, Kang et al. [27] showed that in healthy Korean participants, females scored higher on all temperaments than did males, which is similar to the results of the present study: the cyclothymic temperament resembles items in Lability; depressive, irritable, and anxious temperaments include concepts of Downward Tendency; and items within the hyperthymic temperament is similar to those of Upward Tendency. In addition, mood instability is more likely to be reported by females than males in the general adult population, as well as the clinical adult population in England [7,28]. Moreover, previous research suggests females experience greater seasonal variations in mood and behavior, even in the general population [14,29], which supports our finding. Regarding scores for Childhood Instability, although many studies show that girls experience greater mood instability than do boys [30], there were no gender differences observed in our results. One explanation may be that children in Korea, regardless of gender, are more likely to suppress their emotions in comparison to children in European or North American countries, as Korea has a collectivist culture in which individuals value social harmony than emotional expression [31]. Meanwhile, no score differences were observed across age groups, demonstrating the efficiency and utility of the MIQ-T-SF for measuring mood instability in participants across a wide age range.

Despite the meaningful results, the current study must be interpreted within the context of its design and related limitations. First, as the MIQ-T was originally developed and validated in the Korean population, the MIQ-T-SF was also developed in Korea and involved the Korean general population. As the MI trait may differ across different ethnicities and countries, future research with samples from different ethnic populations is warranted. Translations to other languages (English, Japanese, French, German, Spanish, and Mandarin) are provided in Supplementary Table 3 (in the online-only Data Supplement). Second, because we utilized an online survey platform to recruit participants and collect anonymized data, we could not confirm the absence of psychiatric diagnoses in our sample. Individuals with a history of current or past psychiatric illness may experience more MI than do individuals without such history, which may have inflated certain scores. Nonetheless, the assumption of the MIQ-T-SF is that it includes dimensions within a single trait of MI, and thus, individuals who experience MI will score higher than others on all factors. In addition, the online survey included a screening question regarding the psychiatric history of participants, which would have helped exclude individuals with such a history. Third, due to the anonymized data, test-retest reliability could not be investigated. As an important component of scale validation, this is an area for improvement for future studies. Fourth, as the Childhood Instability factor includes items of a retrospective nature, concerns about accuracy could be raised. However, as these items do not ask about specific recollections, and instead ask participants to broadly recall their own behavior over the course of their childhood, the authors believe that the issue of accuracy is not a big concern. Lastly, the MIQ-T-SF should be investigated in both the patient population and the general, nonpsychiatric population to evaluate its utility in differentiating between the two groups. The MIQ-T had demonstrated its potential in differentiating between diagnosis groups and between the psychiatric and nonpsychiatric samples in the initial development study [12]. It would be worthwhile to assess whether the MIQ-T-SF can also be used to compare scores between patients and controls, which would make it useful in symptom detection, differential diagnosis, and monitoring treatment efficacy. Future studies that address the current limitations and further explore the utility of the MIQ-T-SF are needed.

Despite these limitations, the present study also has some advantages over the original MIQ-T development study. In the original study, items were selected from various, pre-existing questionnaires to develop the MIQ-T and, thus, there was a separate scoring system for specific items. However, the present study used a uniform answering scale from “not at all true=0” to “exactly true=3,” improving the utility of the MIQ-T-SF. As the MIQ-T and MIQ-T-SF exhibit similarities in factorial structure and correlations with other established scales, we believe that the use of a uniform answering scale can be validated. Moreover, the sample was recruited in equal parts by gender and age groups. Given that our sample was balanced, the results can be easily generalized to other Korean individuals, and comparisons between gender and age groups can be considered reliable.

In conclusion, this study presents several important findings. We aimed to develop a MIQ-T-SF while maintaining the five-factor structure and to achieve comparable psychometric properties and construct validity of the full version. Overall, the results provide additional support for the MIQ-T scale, confirming the conceptual unity of the MIQ-T-SF with the MIQ-T, and validating the utility of the shorter version. The MIQ-T-SF appears to be a promising measure that captures the dimensions related to MI and offers a coherent invariant factor structure that is similar to that of the original MIQ-T. The current results indicate that the MIQ-T-SF can reliably and validly assess the MI trait using 17 items, thus improving its efficiency and demonstrating its usefulness as an economical alternative to the full MIQ-T. The brevity of the MIQ-T-SF allows for less item redundancy, less respondent burden, simplified scoring, and shorter administration time in assessments of both the clinical and general populations. The MIQ-T-SF can contribute to both clinical and research procedures as it can be used in time- and cost-intensive research to quickly assess MI and to monitor the treatment progress and symptom reduction in clinical individuals with MI. Various translations are provided in Supplementary Table 3 (in the online-only Data Supplement) for accessibility of the MIQ-T-SF.