2.2.1. Sample source.

The subjects of this study were nursing students in vocational schools in Eastern China. From March to May 2025, purposive sampling was used to select nursing students from 9 medical vocational schools, and we distributed the “Wenjuanxing” (an online survey platform) link to complete the questionnaire. A total of 1,588 questionnaires were collected, with 1,467 valid responses.

2.2.2. Inclusion criteria.

The inclusion criteria included the following:

• Chinese nationality;
• Nursing students currently enrolled in vocational schools;
• Informed consent and voluntary participation in this study;
• The respondent completed the questionnaire by themselves or with assistance from the investigator.

2.2.3. Exclusion criteria.

A total of 1467 valid response questionnaires were collected, and invalid questionnaires were excluded for the following reasons:

• The respondent had been diagnosed with severe mental or physical illness or had limited mobility;
• Questionnaire with missing items;
• Questionnaires showed incorrect answers to ≥2 of the 3 ’trap questions’;
• Questionnaires were completed in less than 180s.

2.3.1. Center for Epidemiological Survey Depression Scale (CES-D).

Depressive symptoms were assessed using the Center for Epidemiological Survey Depression Scale (CES-D) [13], which is by far the most frequently used instrument [14]. The CES-D is a 20-item self-reported questionnaire that evaluates depressive symptoms experienced over the past week (i.e., the recall period is restricted to the preceding 7 days). Comparative analyses with the Hamilton Depression Rating Scale (HAMD) have demonstrated that the CES-D exhibits good validity; thus, it is suitable for application in epidemiological investigations. In this study, the Chinese version of the scale translated by Zhang [15] was adopted. Its reliability and validity had been examined among Chinese adolescents by Chen [16], with a Cronbach’s α coefficient of 0.88 and an average inter-item correlation of 0.26, indicating satisfactory reliability. In large-scale mental health surveys, the CES-D is typically employed as an initial screening instrument: following initial screening, individuals with positive results undergo further diagnostic assessments to confirm potential depressive conditions. According to general research consensus, the CES-D scoring criteria are defined as follows: a score of ≤15 indicates the absence of depressive symptoms; a score ranging from 16 to 19 suggests the possible presence of depressive symptoms; and a score of ≥20 denotes the definite presence of depressive symptoms.

In SD studies, two differing approaches are taken to the cut-off value for SD: the most commonly used definition for SD using CES-D is CES-D ≥ 16 [14,17], but sometimes, a CES-D score≥20 serves as the initial screening threshold [18]. There is no definitive evidence indicating that one cut-off value is superior to the other. Using the commonly applied cutoff for SD in prior research, participants with a CES‑D score≥16 were classified as having SD, while those with a score≤15 were classified as the control group in this study.

2.3.2. Family Adaptability and Cohesion Scale—Chinese Version (FACES II-CV).

The Family Adaptability and Cohesion Scale—Chinese Version (FACES II-CV) consists of 30 items and is divided into 2 dimensions: family cohesion and family adaptability [19,20]. According to the ‘arch model’ [21], the subject families are divided into 16 family types. Those who are in the middle of the 4 types (i.e., Flexible-Connected, Structured-Connected, Structured-Separated, Flexible-Separated) on the two subscales are balanced, showing a moderate emotional distance between family members, both intimate and independent; that is, they have well-adapted, healthy families. Those who are at the extremes of the 4 types (i.e., Chaotic-Disengaged, Rigid-Disengaged, Chaotic-Enmeshed, Rigid-Enmeshed) on the two subscales show extreme levels of family cohesion and adaptability, that is, the lowest level or the highest level, and these families and their members often show diametrically opposite characteristics in intimacy and adaptability. The other 8 types (i.e., Flexible-Disengaged, Structured-Disengaged, Chaotic-Separated, Rigid-Separated, Chaotic-Connected, Rigid-Connected, Flexible-Enmeshed, Structured-Enmeshed) are intermediate on one subscale and extreme on the other and are classified as being of an intermediate type.

FACES Ⅱ is widely used in Western countries. Fei [22] translated the scale into Chinese, revised it three times, and assessed its reliability and validity within Chinese families. The results showed that the scale demonstrated good content validity and internal consistency, and Cronbach’s α coefficients for the two dimensions were 0.67 and 0.72, respectively.

2.3.3. Dysfunctional Attitude Scale form A (DAS-A).

The Dysfunctional Attitude Scale form A (DAS-A) is a self-report scale designed to measure the presence and intensity of dysfunctional attitudes [23]. The DAS-A consists of 40 items, and each item consists of a statement and a 7-point Likert scale (7 = fully agree; 1 = fully disagree). The total score is the sum of the 40 items, with a range of 40–280. The higher the score, the more dysfunctional attitudes an individual possesses [24]. The 40 items can be divided into eight dimensions: Vulnerability, Perfectionism, Approval and Disapproval, Compulsivity, Dependence, Autonomy Attitudes, Need for Approval, and Cognitive Philosophy. The higher the total score, the more severe the cognitive distortion. Cai [25] brought together clinical psychologists and bilingual linguists from both China and Canada to conduct a series of iterative translations and back-translations of all items, ultimately creating the Chinese version of the Dysfunctional Attitude Scale. This scale underwent pilot testing and validation with Chinese adolescents, yielding a total scale reliability coefficient of 0.88 and a test-retest reliability coefficient of 0.84.

2.3.4. Chinese Adolescent Social Support Scale (CASS).

The Chinese Adolescent Social Support Scale (CASS) was developed by Ye [26] in 2008. It consists of 17 items, including three dimensions, subjective support, objective support, and support utilisation, and is used to assess the extent to which individuals receive and utilise social resources. This instrument uses a 5-point Likert scale (1 = not applicable, 2 = somewhat not applicable, 3 = indeterminate, 4 = somewhat applicable, and 5 = applicable). The higher the score, the more social support the individual has. According to the total score on the scale, the level of support received is divided into 3 categories: low (total score<50), medium (50–77), and high (>77). The internal consistency of the whole scale is 0.907, and the reliability of each subscale is 0.846, 0.806, and 0.838, respectively. The KMO is 0.915, indicating good structural validity. In this study, Cronbach’s α coefficient for this scale was 0.77.

2.3.5. 10-item Connor–Davidson Resilience Scale (CD-RISC-10).

The Connor-Davidson Resilience Scale (CD-RISC) was developed by Connor and Davidson [27]. Campbell-Sills [28] simplified the scale, resulting in the 10-item CD-RISC-10. Subsequently, Yu [29] translated and culturally adapted this 10-item version into Chinese, establishing the Chinese version of the CD-RISC-10, and validated it in Chinese populations. CD-RISC-10 (Chinese version) scored using a 5-point Likert scale (0 = Never, 1 = Rarely, 2 = Sometimes, 3 = Often, 4 = Always). The scale initially included 5 factors: tenacity, tolerance of negative affect, positive acceptance of change, control, and spiritual beliefs. It includes the 3 dimensions of tenacity, strength, and optimism and has good psychometric properties. This study used a 10-item short version of the Resilience Scale, extracting items 1, 4, 6, 7, 8, 11, 14, 16, 17, and 19 from the original 25 items, with a total score ranging from 0 to 40. Higher scores reflect higher levels of resilience. Cronbach’s α coefficient for this study was 0.942.

2.3.6. Chinese Big Five Personality Inventory—brief version (CBF-PI-B).

Taking the Big Five model as the theoretical framework and building upon the Big Five Inventory (BFI) developed by John [30], Wang [31,32] compiled a Chinese version of the Big Five Personality Inventory. Through statistical methods, they further selected appropriate items to form a short version, namely the Chinese Big Five Personality Inventory-Brief Version (CBF-PI-B). This inventory consists of 40 items and including five dimensions: CBF-PI-B-Openness, CBF-PI-B-Conscientiousness, CBF-PI-B-Extraversion, CBF-PI-B-Agreeableness, and CBF-PI-B-Neuroticism. Each dimension is measured using 8 items and a 6-point Likert scale (1 = very inconsistent, 2 = relatively inconsistent, 3 = slightly inconsistent, 4 = slightly consistent, 5 = relatively consistent, 6 = very consistent). The correlation between each factor in the brief version (CBF-PI-B) and the corresponding factor in the full version (CBF-PI) is above 0.85. Cronbach’s α coefficient for the five dimensions of the brief version is above 0.75 [33].

4.2.1. Comparison of general demographic characteristics.

A comparison was made between individuals with subthreshold depression and those without, using chi-squared tests and t-tests to determine significant differences. The findings of the chi-squared test demonstrated significant disparities between the two groups with regard to gender, maternal level of educational attainment, parental marital status, and family type. The incidence of subthreshold depression was found to be significantly higher among female students than among their male counterparts. This finding is consistent with the results of previous studies [44,45]. The observed disparity may be attributed to women having greater susceptibility to emotionally triggering external factors, as well as the broader societal expectations placed on them, which contribute to increased academic and employment pressures. However, given the preponderance of women within the nursing profession, the possibility of sampling bias cannot be discounted. Further studies are required to validate these findings.

4.2.2. Comparison of family functioning-related indicators.

This study found that students whose mothers had attained a higher level of education were less likely to experience subthreshold depression. However, no significant association was observed between fathers’ educational level and subthreshold depression. This pattern may be closely related to mothers’ familial roles, parenting approaches, and mental health awareness. Within the context of traditional Chinese social culture, the responsibility for child-rearing is shouldered by mothers in many households. Individuals with higher levels of education have been shown to have greater awareness of mental health issues, which may result in enhanced ability to recognise emotional distress in their children and provide timely and appropriate support. However, this does not imply that the role of the father is unimportant. A father’s level of education can indirectly affect his children via their mother. Consequently, it is necessary for both parents to pay close attention to their children’s mental health status and to assist in reducing negative emotions. Contrary to the findings of previous studies, our research demonstrated a higher prevalence of subthreshold depression among students from families characterised by harmonious parental marital relationships. This phenomenon may be attributed to the fact that families with stable marriages often have higher expectations for their children. Consequently, children who are influenced by this type of family atmosphere tend to pursue perfection, thereby experiencing greater academic or behavioural pressure. Additionally, children from families with harmonious marriages may have less exposure to adversity, rendering them more vulnerable to depressive emotions when facing difficulties [46]. Therefore, it is essential for parents to be attentive to their children#39;s emotional needs and to assist them in coping with stress. Based on our study, we hypothesise that family type exerts a certain influence on subthreshold depression (SD) among vocational nursing students. The SD group was primarily characterised by mid-range family types (44.5%). As demonstrated in Table 2, the levels of family cohesion and adaptability exhibited by students in the SD group were found to be significantly lower in comparison to those observed in the normal group. In accordance with the principles outlined by Olson’s [21] Circumplex Model of Marital and Family Systems, mid-range family typologies are distinguished by an imbalance between cohesion and adaptability. This implies that one dimension remains within the standard range, while the other exhibits an excessively high or low value, thereby signifying impairments in specific domains of family functionality. Subsequent analysis indicated that the three most prevalent family subtypes among nursing students with SD were Rigid-Separated (16.6%), Flexible-Enmeshed (15.3%), and Rigid-Disengaged (13.7%). Among these, extreme family types demonstrated the poorest overall functioning. The findings of this study indicate that within the SD group, family relationships are characterised by emotional independence, accompanied by the maintenance of appropriate boundaries. However, certain students demonstrated an excessive detachment from, or over-dependence on, their parents, reflecting either weak or highly entangled emotional connections. The transition of late adolescents towards independence is accompanied by a psychological shift that marks a departure from the authority of their parents. This process is frequently referred to as psychological ‘weaning’. This dynamic can result in reduced communication with parents, resistance against parental authority, and, in the most severe cases, emotional distancing. These developmental shifts frequently result in a reduction in familial cohesion. Conversely, some families exhibit a lack of clearly delineated personal boundaries, resulting in elevated levels of emotional and behavioural enmeshment, over-reliance on one another, and difficulties in independent decision-making or problem-solving.

Furthermore, families in the SD group demonstrated significantly lower levels of cohesion and adaptability, which resulted in impaired communication, emotional alienation, inflexible family roles, and an inability to adjust effectively to developmental changes or external stressors. These factors collectively compromise overall family functioning. In comparison to their counterparts enrolled at universities, vocational students generally encounter reduced academic pressure and more leisure time. However, it is important to note that many individuals become excessively engaged in online games, which has the potential to place further strain on family relationships. Some studies have indicated that internet addiction has the potential to reduce parent–child communication and shared daily experiences, which can result in family conflict resolution becoming more challenging [47]. This behaviour has been linked to delayed psychosocial maturation due to prolonged exposure to virtual environments. This may also contribute to the development of subthreshold depression in this population. The enhancement of family cohesion and adaptability has been demonstrated to be a means of reducing depressive symptoms and promoting physical health among adolescent students [35,36].

4.2.3. Comparison of DAS, social support, resilience, and personality traits between the two groups.

As demonstrated in Table 2, the DAS score of nursing students in the SD group was found to be significantly higher than that in the non-SD group. Furthermore, nursing students who exhibited elevated levels of depressive symptoms also demonstrated a higher level of dysfunctional attitudes, a finding that is consistent with the results of previous studies. Dysfunctional attitudes have been observed to manifest with notable stability within the cognitive structure of adolescents. In the event of adverse life experiences, such as those previously outlined, the potential for the onset of dysfunctional attitudes in adolescents is increased. This can result in a tendency to interpret external information in a negative and distorted manner. This, in turn, gives rise to a series of depressive symptoms or emotions.

Additionally, the levels of social support and resilience were significantly lower in the SD group than in the control group. Numerous studies have demonstrated that a low level of social support is closely associated with an increased risk of depression. In circumstances where social support is inadequate, individuals may experience feelings of isolation and helplessness and find themselves lacking the necessary resources to cope with stress and adversity. This, in turn, can increase their vulnerability to depressive symptoms. Resilience has been identified as a critical protective factor for individuals’ mental health, as it has been demonstrated to serve as a buffer against the adverse effects of challenging circumstances. In line with the findings of earlier research, this study demonstrates a negative correlation between resilience and emotional disorders. Vocational nursing students constitute a relatively distinctive student group. Faced with demanding academic workloads, relatively low levels of academic achievement, high employment pressure, and the imminent responsibility of engaging in patient care and life-saving tasks, these students often experience a sustained high-pressure environment. Consequently, they demonstrate a heightened vulnerability to depressive symptomatology in comparison to the general population.

Regarding personality traits, the SD group demonstrated lower scores in comparison to the non-SD group across all factors, with the exception of the neuroticism dimension of the CBF-PI-B. Individuals who score higher for the neuroticism factor tend to be more susceptible to negative emotions such as anxiety and depression.

4.2.4. Related factors in subthreshold depression among vocational nursing students in eastern China.

Multivariable binary logistic regression was employed in this study to analyse the associations between respondents’ demographic characteristics, scale scores, and the associated factors of subthreshold depression. Independent associations were further quantified using odds ratios (ORs) and 95% confidence intervals (CIs). Notably, all 95% CIs for these ORs excluded the null value of 1, reinforcing the statistical stability and reliability of these independent effects. Regression analysis revealed that subthreshold depression in nursing students in vocational schools is closely associated with gender, dysfunctional attitudes, CBF-PI-B-Neuroticism trait, social support and resilience. Compared with males, females have a significantly higher odds of depression. This phenomenon can be partly attributed to women’s tendency to exhibit heightened emotional intensity and sensitivity [48]. In line with this gender-related pattern, research has shown that female vocational nursing students are more likely to experience depression than their male counterparts. This phenomenon has been attributed to various factors, such as academic performance, physical appearance, lifestyle habits, and cumulative pressure from academic and daily life [49]. Further studies have indicated that this gender discrepancy also applies to subthreshold depression, with female students demonstrating a higher tendency toward this condition than their male counterparts. Therefore, teachers and parents should pay more attention to female students. Psychological counselling and other approaches can alleviate psychological pressure, provide timely assistance in resolving difficulties, and identify subthreshold depressive tendencies early on. Effective intervention should be implemented promptly for students exhibiting subthreshold depression. Dysfunctional attitudes were independently and significantly positive associated with SD. According to Beck’s cognitive model of depression, depressive symptoms can be promoted by dysfunctional attitudes when triggered by stressful life events [50]. There is ample evidence that the content of dysfunctional thinking is associated with vulnerability to major depression [51,52]. This study confirmed that, as a high-risk population for MDD, individuals with subthreshold depression exhibited a significant positive correlation between dysfunctional attitudes and subthreshold depression. Therefore, greater attention should be paid to the population with psychological subhealth, especially adolescents in the critical period of cognitive development. Structured cognitive interventions should be conducted among this group to improve their cognitive regulation ability, thereby preventing the pathological transition from subthreshold depression to MDD. Among the various personality trait dimensions, the CBF-PI-B-Neuroticism factor significantly influences the occurrence of subthreshold depression in nursing students. Those with high neuroticism scores experience negative emotions such as anxiety and depression more readily. They also exhibit heightened sensitivity to stress and emotional stimuli, display greater emotional volatility, and are more prone to negative emotional states. Concurrently, research indicates that neuroticism may be associated with functional abnormalities in certain neurotransmitters (such as serotonin), which are closely linked to the development of depression.

Furthermore, regression analysis showed that after controlling for potential confounding variables, social support and resilience both entered the regression equation and were independently and negatively associated with subthreshold depression. These findings extend the correlational results obtained in the previous comparative analysis and confirm that social support and resilience may serve as potential protective factors against subthreshold depressive symptoms, rather than merely reflecting group differences. The independent predictive roles of these two factors suggest that interventions targeting the enhancement of social support resources and the improvement of psychological resilience may effectively reduce the risk of subthreshold depression among vocational nursing students. Taken together, these results highlight the importance of integrating both external supportive resources and internal psychological capacities into preventive strategies for subthreshold depression in this high-risk population.

The factors influencing subthreshold depression among vocational college nursing students are multifaceted and complex. While earlier studies suggested that factors such as place of birth, academic year, and being an only child may impact subthreshold depression, this study found these to be non-significant. The regression equation revealed that gender and neuroticism were the only significant factors. This discrepancy may be attributed to the geographical location of the survey population and the particular educational levels involved. Further validation of the potential for sampling bias is required.