Childhood trauma experience, which is identified as a detrimental experience of human development (Beilharz et al., 2020), is closely related to several internalizing problems, including depression, anxiety, and stress (Ma et al., 2020; Wang et al., 2022b). Furthermore, a number of research have identified a correlation between childhood trauma and problematic smartphone use (PSU) (Forster et al., 2021; Geng et al., 2022). PSU is commonly classified as a behavioural addiction, although it lacks official recognition in the DSM-5 (Harris et al., 2020). However, there is a scarcity of research examining the intricate interplay between internalizing problems (such as depression, anxiety, and stress) and PSU in individuals who have undergone childhood trauma. This lack of investigation has resulted in a significant deficiency in the treatment and mitigation of these mental disorders among individuals with childhood trauma.

Multifunctional smartphones are rapidly developing and becoming increasingly popular among people, which provide numerous gratifications, including entertainment, social interaction, and information finding, etc. (Leftheriotis and Giannakos, 2014). However, increasing research indicates that features of smartphones (convenience, portability, and privacy) may facilitate PSU (Billieux et al., 2015). In other words, receiving rewards easily from the smartphone may increase the frequency of smartphone usage behaviours, leading to unfavourable outcomes for physical and mental health, such as decreasing work efficiency (Joshi et al., 2022), the rising risk for anxiety and depression (Zhang et al., 2018), insomnia, earache, and headache (Sahin et al., 2013). Notably, Olson et al. (2022) reviewed the articles published from 2014 to 2020 worldwide and demonstrated that PSU is increasing across the world, and China, Malaysia, and Saudi Arabia exhibit the highest severity. Meanwhile, as another systematic review suggested, young and highly educated people are especially prone to suffer from PSU (Busch and McCarthy, 2021). Besides, a long-term observation indicated that college students reported a rising proportion of PSU and increasing negative outcomes (such as increasing boredom, emptiness, and anxiety without smartphones) from 2007 to 2016 (Carbonell et al., 2018). More alarmingly, during the COVID-19 pandemic, the smartphone has become the main information resource and social tool for college students, which further increases the risk of PSU among college students (Li et al., 2021). As a longitudinal study reported, PSU can disrupt the sleep routine of college students and seriously influence their academic performance (Lin and Zhou, 2022). Indeed, PSU among college students deserves more attention.

Depression, anxiety, and stress, categorized as internalizing problems, are common among college students with the prevalence rate reaching 29 % (anxiety), 37 % (depression), and 23 % (stress) (Wang et al., 2021). Evidence showed that these internalizing problems share a close relationship with PSU (Elhai et al., 2018). As the use and gratification theory states, one's social and psychological status may influence one's motivations in communication, which further affects one's choice and use of the communication channels (online or interpersonal) as well as the subsequent outcomes (Katz et al., 1973). In other words, individuals struggling with negative status such as depression, anxiety, and stress are more prone to avoid face-to-face communication and use a smartphone for communication, which may increase the risk of PSU (Elhai et al., 2016). Studies so far have provided us with multiple supportive evidence. For example, one longitudinal research has declared a close relationship between PSU and internalizing problems (depression, anxiety, and stress), stating that the negative mood state can precisely predict smartphone use in the corresponding days (Rozgonjuk et al., 2018). One meta-analysis, containing the results of 27 studies, identified that depression and anxiety shared close associations with PSU (Augner et al., 2023). Similarly, one study that employed meta-analysis found the relation between stress and PSU (Vahedi and Saiphoo, 2018). Evidence from longitudinal design also supported the close association between depression and PSU (Cui et al., 2021), anxiety and PSU (Xie et al., 2023a), and stress and PSU (Zhao et al., 2021).

The associations between depression, anxiety, stress, and PSU may differ across different genders. Compared with females, males are more likely to develop PSU (Chi et al., 2020). Previous literature also found that in college, males and females had different prevalences of depression, anxiety, and stress (Ramón-Arbués et al., 2020). A study, conducted on college students whose scores on the smartphone addiction scale met the cut-off standard, found that females and males differed in their purpose of using smartphones, which is related to diverse internalizing problems (anxiety for males and depression for females) (Chen et al., 2017). Consistently, the research of Tu et al. (2023) identified the moderating effect of gender on the relation between stress and PSU.

In conclusion, previous studies have identified a strong interconnection between internal problems and PSU through extensive research. Furthermore, research also indicates that the relationship between internal problems and PSU may vary between males and females. However, there is a dearth of studies investigating the aforementioned topics from the perspective of symptoms, ignoring the complex associations between symptoms of depression, anxiety, stress, and PSU. Thus, the present research would delve deeper into the associations between symptoms of depression, anxiety, stress, and PSU, as well as the possible gender differences through network analysis.

Childhood trauma refers to the acts given by the individual who had a duty to take care of the child, including physical abuse, emotional abuse, sexual abuse, physical neglect, and emotional neglect, which can cause actual or potential harm to the development, health, or dignity of the child (Wang et al., 2019). Experience of childhood trauma can disrupt victims' positive self-construct, hinder the health development of cognitive function and emotion regulation ability, and increase the risk for both internalizing problems and PSU (Ma et al., 2020).

Specifically speaking, according to the self-mediation theory proposed by Kohut (1977), addictive behaviours (including substance abuse, PSU, etc.) result from the inadequate development of self-structure, which can be attributed to the experience of childhood trauma (Flores, 2001). In line with the theory, research stated that cumulative childhood trauma significantly and positively predicted PSU among college students through the mediating effect of self-esteem and self-concept (Xie et al., 2023b). Meanwhile, a two-wave longitudinal study also stated that prior experience of childhood trauma can increase students' subsequent engagement in PSU (Geng et al., 2022). However, previous studies that examined the association between childhood trauma and PSU, simply calculated the relation between the scores on the childhood trauma scale and the mobile phone addiction scale (Dvir et al., 2014; Ma et al., 2020; Xie et al., 2023b). This approach overlooked the fact that a significant proportion of participants did not meet the criteria for childhood trauma victims, which severely curtailed the clinical applicability of the findings.

Apart from that, robust evidence has proved that exposure to childhood trauma may increase individuals' vulnerability to depression, anxiety, and stress by disrupting the emotional regulation ability and preventing positive self-construction (Dvir et al., 2014; Vibhakar et al., 2019; Wang et al., 2022b). Despite all these findings, to our best knowledge, there existed almost no research taking childhood trauma, emotional disorders (depression, anxiety, stress), and PSU into consideration at the same time. This shortage may hinder clinicians from designing proper interventions for PSU among individuals exposed to childhood trauma.

Former research perceived the traditional perspective as holding the belief that symptoms in mental disorders existed separately and could be attributed to a common cause. Based on the diagnostic system of DSM-5, the traditional perspective contributed greatly to the diagnosis and categorization of mental disorders, yet ignored the interaction and triggering effects between different symptoms (Borsboom, 2021). To fill this gap, the network analysis approach can serve as a suitable tool to clarify the complex interaction model between different symptoms in comorbid mental disorders (Jones et al., 2021). Nevertheless, to our best knowledge, there has not been any research using the network approach to explore the relation between depression, anxiety, stress, and PSU when considering the influence of childhood trauma. Indeed, considering the close relation between depression, anxiety, stress, and PSU (Rozgonjuk et al., 2018) and the higher risk for both PSU and internalizing problems among individuals suffering from childhood trauma (Ma et al., 2020; Wang et al., 2022b), it is necessary to further clarify the possible intensifying interaction between PSU and internalizing problems, especially among college students exposed to childhood trauma.

Hence, to address the limitations in the former studies and to clarify the relation between childhood trauma, depression, anxiety, stress, and PSU, the current study, using network analysis, made a comparison between college students with a history of childhood trauma and their normal counterparts. It must be noted that the depression and anxiety in the current study were measured by self-report scales. It only reflected the levels of depressive and anxious symptoms, not clinical depression and anxiety. The aims and hypotheses of the current study are as follows:

Aim 1: Comparing the severity of depression, anxiety, stress, and PSU between college students with and without childhood trauma to verify that childhood trauma can have a serious influence on individuals, leading to more severe internalizing problems and PSU.

Hypothesis 1

Previous studies found that childhood trauma can increase the risk for depression, anxiety, stress, and PSU (Ma et al., 2020; Wang et al., 2022b). Indeed, we hypothesize that compared to their normal counterparts, college students exposed to childhood trauma exhibited higher prevalence rates of depression, anxiety, stress, and PSU and scored significantly higher on all symptoms of these disorders.

Aim 2: Examining whether sex differences exist in the trauma group and their normal counterparts.

Hypothesis 2

Previous literature suggests that females may be more susceptible to depression, anxiety, stress, and PSU (Seehuus et al., 2021; Wang et al., 2022a). Thus, we hypothesize that females score higher in the mean levels of symptoms of DASS-21 and PSU among both the trauma group and the no-trauma group.

Aim 3: Comparing the symptom network between college students with and without childhood trauma and identifying the symptoms that connect the complex comorbidity network of depression, anxiety, stress, and PSU to provide an effective intervention target.

Hypothesis 3

According to the use and gratification theory, PSU can be viewed as the outcome of a negative mental status (Katz et al., 1973). Therefore, we hypothesize that there exist more bridge symptoms in the network of depression, anxiety, stress, and PSU among college students with childhood trauma compared to their counterparts.