Factors affecting sibling bullying and its association with self-esteem and depression in middle school students

Abstract

Sibling bullying is an unwanted aggressive behavior of a sibling that is associated with peer bullying and emotional problems. However, the prevalence of sibling bullying, the factors that affect this condition, and its impact on depression and self-esteem are understudied, especially in Thailand. This study aims to examine the prevalence of sibling bullying, factors that affect sibling bullying, and its association with self-esteem and depression during the pandemic. From January to February 2022, a cross-sectional study was conducted in grades 7–9 (age 12–15 years) who had at least one sibling. Demographic characteristics, sibling bullying, self-esteem, and depression were collected using the revised Olweus bully/victim questionnaire, the Rosenberg self-esteem scale, and Patient Health Questionnaire-9, respectively. Binary logistic regression was analyzed to determine associations between sibling bullying and outcomes. Of 352 participants (30.4% female), 92 (26.1%) were victims and 49 (13.9%) were bullies of sibling bullying in the previous 6 months. Factors associated with an increased risk of being victims included female (OR = 2.46; 95%CI 1.34–4.53), peer victimization (OR = 12.99; 95%CI 5.27–32.04), domestic violence (OR = 4.48; 95%CI 1.68–11.95), and perpetrating sibling bullying (OR = 9.81; 95%CI 4.62–20.81). Factors associated with an increased risk of depression were female (OR = 2.59; 95%CI 1.57–4.26), sibling bullying victimization (OR = 2.08; 95%CI 1.22–3.56), physical abuse (OR = 9.50, 95%CI 1.13–79.71) and domestic violence (OR = 3.44; 95%CI 1.40–8.45).

  Conclusion: Sibling bullying was not uncommon in Thai young adolescents and was associated with female, peer bullying, domestic violence, and depression. Such associations should be identified early so preventive measures and management could be properly implemented.

What is Known: • Sibling bullying increases the risk for engaging in peer bullying, aggressive behaviors, violence, and emotional difficulties during life course trajectories. • Victims of sibling bullying are at increased risk of depression, anxiety, mental distress, self-harm, and decreased well-being.

What is New: • The rate of sibling bullying in Thai middle school students, even during the pandemic, was comparable to previous studies of different cultural backgrounds without the pandemic. • Victims of sibling bullying were associated with female sex, peer victimization, domestic violence, perpetrating sibling bullying, and depression. Perpetrating sibling bullying was also associated with bullies in cyberbullying.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00431-023-05015-y.

Introduction

Sibling bullying is an unwanted aggressive behavior of a sibling that is involved in an observed or perceived power imbalance between siblings and appears to occur repeatedly [1]. Sibling bullying is one of the common forms of violence in our society, approximately 4–50% in western countries [1–6]. This type of bullying can have negative impacts not only on those who are victimized, but also on individuals who are perpetrators of the situation [5, 6]. Although the causal relationship between sibling bullying and psychological outcomes cannot be drawn from current evidence and the nature of such a relationship is unclear, victims of sibling bullying are more likely to have behavioral problems, depression, anxiety, internalizing problems, externalizing problems, mental distress, physical injury, self-harm, suicidal ideation, decreased well-being, and low self-esteem [1, 2, 5–7]. Additionally, those who bully their siblings tend to also have a higher risk of depression, anxiety, externalizing problems, psychological distress, and suicidal ideation [6, 7]. Some of the aforementioned evidence on the association between sibling bullying and emotional difficulties came from cross-sectional studies. Recent research has demonstrated longitudinal impacts of sibling bullying during childhood and early adolescence on emotional difficulties and mental health outcomes in later adolescence and young adulthood, even after adjustment for preexisting childhood factors and peer bullying in prospective cohorts [2, 6, 8]. Furthermore, sibling bullying increases the risk of participating in peer bullying and is independently related to concurrent and early adult emotional problems [5, 6, 8]. Such evidence might explain why sibling bullying and emotional difficulties are related. Therefore, individuals who are involved in sibling bullying can later participate in other types of bullying, aggressive behaviors, and violence, as well as worse mental health outcomes during their life course trajectories [5, 6, 8].

Similarly to studies conducted in western countries, research in non-western countries, including China, Turkey, Pakistan, Vietnam, and Algeria, has reported a prevalence of sibling bullying, including victimization and perpetration, ranging from 12.5 to 53.8% [9–14]. Furthermore, sibling bullying was also associated with negative mental health outcomes, including anxiety, depression, reduced well-being, psychological distress, and disengagement [9, 10, 13, 14], as well as other types of bullying, such as peer bullying, peer victimization, and delinquent behaviors in schools [12–14].

The COVID-19 pandemic has created a unique situation in which children tended to spend significantly more time with their siblings, providing an opportunity to investigate the prevalence rates of sibling bullying during the pandemic. These rates may differ from what is typically observed. A longitudinal study conducted in the United Kingdom with children and adolescents with special educational needs and disabilities found that these individuals tended to be victimized by their siblings, especially as the lockdown progressed [15]. However, when schools were fully reopened, victimization declined, but the rate was still higher compared to the first month of lockdown [15]. Another study found a higher prevalence of sibling bullying during the pandemic compared to before it [16]. However, children’s subjective well-being scores during COVID-19 were lower than those before the pandemic, regardless of their bullying status [16]. Due to the lack of research on the prevalence of sibling bullying during the pandemic and its association with mental health outcomes, particularly depression and self-esteem, investigating this issue is crucial to better understand the possible effects of the pandemic on sibling bullying and depressive symptoms. In addition, it could potentially help develop effective interventions to address any increase in sibling bullying, particularly during such circumstances.

Furthermore, sibling bullying is considered a family issue that is often overlooked and not explored [3], particularly in Southeast Asian countries, including Thailand, where the prevalence of sibling bullying, factors that affect sibling bullying, and its association with self-esteem and depression may be similar or different from western countries, especially during the COVID-19 pandemic. To the best of our knowledge, no empirical research has been conducted in Thailand investigating the prevalence of sibling bullying and the relationship between sibling bullying and emotional difficulties, as well as self-esteem, despite evidence from worldwide studies, mostly without the pandemic. Therefore, it is imperative to investigate this phenomenon in the Thai context and during the pandemic era. Understanding these knowledge gaps can provide useful information to stakeholders who are responsible for preventing, identifying, and managing the consequences of sibling bullying. This study aims to address three research questions:

1. What was the prevalence of sibling bullying in Thailand during the COVID-19 pandemic?

2. What were the factors that were associated with sibling bullying, both victimization and perpetration, in separate models?

3. Was sibling bullying associated with low self-esteem and depression during this specific situation?

As the existing literature in both western and non-western countries mentioned above, it is unlikely that the prevalence and relationship between sibling bullying and emotional difficulties in Thailand would differ significantly from the findings of previous studies. Therefore, we hypothesized that the prevalence of sibling bullying in this study may be similar to or possibly slightly higher than the rates reported in other studies conducted at different times without the pandemic. Regarding factors associated with sibling bullying, we hypothesized that victims of sibling bullying tended to be associated with perpetrating sibling bullying, as often observed in the context of other types of bullying. Additionally, victims of sibling bullying were more likely to experience peer victimization. Furthermore, we predicted that sibling bullying, particularly victimization, was associated with a greater risk of depression and low self-esteem.

Materials and methods

Study participants

From January to February 2022, a cross-sectional study was conducted in grades 7–9 (age 12–15 years) who had at least one sibling. Due to closing schools during the Coronavirus Omicron variant of the pandemic at that time, to reach middle school students, we finally were in contact with teachers from three public schools in Bangkok using a convenient sampling method. Information about this study was sent online to potential participants individually. If they were interested in participating in this study, the study participants and their parents gave their assent and written informed consent, respectively. Of the 473 potential participants who were initially interested in participating in the study, 121 did not have siblings, so they were excluded from this study. In total, 352 study participants were included in the study. This study was approved by the Institutional Review Board of the Faculty of Medicine of Chulalongkorn University (number 588/64).

Demographic characteristics

We collected demographic data including sex (0 = female, 1 = male), school (0 = Wat Ratchabophit School, 1 = Surasak Montri School, 2 = Triam Udom Suksa Nomklao School), grade (0 = grade 7, 1 = grade 8, 2 = grade 9), birth order (0 = firstborn, 1 = second born, 2 = third born, 3 = fourth born and more), number of siblings (0 = no siblings, 1 = 1 sibling, 2 = 2 siblings, 3 = 3 siblings, 4 = more than 3 siblings), parental marital status (0 = living together, 1 = separated, 2 = divorced), parental education (0 = below bachelor’s degree, 1 = bachelor’s degree, 2 = master/doctor degree), and income (0 =  < 15,000, 1 = 15,001–25,000, 2 = 25,001–35,000, 3 = 35,001–50,000, 4 =  > 50,000 Baht/ month).

Bullying

With respect to sibling bullying, we used the Thai version of the revised Olweus bully/victim questionnaire, which was translated and adapted by Tapanya S and had a reliability score of 0.75 [17, 18]. The questionnaire consists of various types of sibling bullying including physical, verbal, relational, and property damage. Details of sibling bullying for both victims and bullies in sibling bullying are displayed in eTables 1 and 2. Furthermore, the frequency of those who engaged in bullying (bullies) and being bullied (victims) in the past 6 months was obtained based on a 5-point Likert scale as follows: 1) never, 2) only once or twice, 3) 2–3 times a month, 4) about once a week, and 5) several times a week. Those who rated the frequency of bullying of either type as described in eTables 1 and 2 that occurred at least 2–3 times a month in the past 6 months were classified as victims or bullies in sibling bullying [17, 18].

Furthermore, peer bullying, cyberbullying, physical abuse by parents, and domestic violence were also determined, as these variables were more likely to be associated with sibling bullying and outcomes of interest [1, 4, 5]. To determine peer bullying, cyberbullying, physical abuse by parents, and domestic violence, the researcher asked the following questions: 1) How often have you been bullied by your friends at school in the last 6 months? (peer victimization), How often have you been involved in bullying your friends at school in the last 6 months? (perpetrating peer bullying); 2) How often have you been cyberbullied in the last 6 months? (cybervictims), How often have you been involved in cyberbullying in the last 6 months? (cyberbullies); 3) How often have your parents physically abused you in the last 6 months? (physical abuse by parents); and 4) In the last six months, how often have your parents engaged in any abusive behaviors towards each other, including insults, physical harm, verbal attacks, or emotional manipulation? (domestic violence). The frequency of response options was based on a 5-point Likert scale as follows: 1) never, 2) only once or twice, 3) 2–3 times a month, 4) about once a week, and 5) several times a week.

Self-esteem

We evaluated the self-esteem of the study participants using the Rosenberg self-esteem scale, Thai version [19]. It consists of 10 questions where participants had to rate how they felt about themselves based on a 4-point Likert scale ranging from strongly agreeing to strongly disagreeing. All questions were summed to a total score of 10 to 40. Self-esteem was finally divided into 3 groups, including high self-esteem (total score 31–40), moderate self-esteem (total score 21–30), and low self-esteem (total score10-20) [20]. In this study, those who scored in the moderate to high range of self-esteem were classified as having self-esteem.

Depression

We evaluated the depressive symptoms of the study participants using the Patient Health Questionnaire-9 (PHQ-9), Thai version [21, 22]. Although this questionnaire is frequently used to assess depressive symptoms in adults, it has also been shown to be an effective tool for evaluating depression in adolescents around the world [23–25]. The questionnaire contains 9 questions about depressive symptoms. Participants rated how often their depressive symptoms occurred in the past 2 weeks based on a 4-point Likert scale as follows: 0) none, 1) rarely, 2) often and 3) always. Finally, a total score was calculated based on all questions and ranged from 0 to 27. Participants who scored at least 10 were classified as having depression. In this study, Cronbach's Alpha coefficient for this questionnaire was 0.868.

Statistical analysis

Demographic data and prevalence of sibling bullying are shown as frequency and percentage in Table 1, eTables 1 and 2. The associations between bullying in siblings, demographic characteristics, self-esteem, and depression were analyzed using univariate analyzes, mainly the Chi-square test. Associations with a p-value of less than 0.2 in the univariate analysis were finally included in the binary logistic regression analysis adjusting for sex, number of siblings, parental education, parental marital status, peer bullying, physical abuse, and domestic violence. The results are displayed as adjusted odds ratios (ORs) with 95% confidence intervals (CIs) in Tables 2, 3, 4 and eTable 3. Associations with a p-value of less than 0.05 were considered significant. All statistical analyzes were performed with SPSS version 28 (IBM Inc., Bangkok, Thailand) for Windows with the support of Chulalongkorn University.

Table 1.

Demographic characteristics of the study participants

Demographic data	Frequency	Percent (%)
Birth order
- Firstborn	137	38.9
- Second born	159	45.2
- Third born	47	13.4
- Fourth born and more	9	2.6
School
- Wat Ratchabophit School	190	53.9
- Surasak Montri School	66	18.8
- Triam Udom Suksa Nomklao School	96	27.3
Grade
- Grade 7	89	25.3
- Grade 8	176	50
- Grade 9	87	24.7
Parental marital status
- Living together	270	76.7
- Separated	44	12.5
- Divorced	38	10.8
Paternal education
- Below bachelor's degree	217	61.6
- Bachelor’s degree	100	28.4
- Master/doctor degree	35	9.9
Maternal education
- Below bachelor’s degree	180	51.2
- Bachelor’s degree	136	38.6
- Master/doctor degree	36	10.2
Paternal income
- < 15,000฿a	117	33.2
- 15,001–25,000฿	99	28.1
- 25,001–35,000฿	45	12.8
- 35,001–50,000฿	47	13.4
- > 50,000฿	44	12.5
Maternal income
- < 15,000฿	145	41.2
- 15,001–25,000฿	98	27.8
- 25,001–35,000฿	48	13.6
- 35,001–50,000฿	35	9.9
- > 50,000฿	26	7.4

^a1 Euro = 37.63 Baht

Table 2.

Factors associated with sibling bullying (victims)

Variables​	Wald​	df​	p-value​	OR​	95% CI of adjusted OR​
					Lower​	Upper​
Female	8.437​	1​	0.004​	2.463​	1.341​	4.526​
Peer bullying (victims)​	31.001	1​	< 0.001	12.991​	5.268​	32.038​
Domestic violence​	8.993	1​	0.003​	4.482​	1.681​	11.947​
Sibling bullying (bullies)​	35.377​	1​	< 0.001	9.808​	4.622​	20.814​

Dependent variable: sibling bullying (victim), adjusted analyzes based on binary logistic regression models including number of siblings, parental education, parental marital status, victims of cyberbullying, and physical abuse as covariates​

Table 3.

Factors associated with sibling bullying (bullies)

Variables​	Wald​	df​	p-value​	OR​	95% CI of adjusted OR​
					Lower​	Upper​
Cyberbullying (bullies)​	13.042	1​	< 0.001	11.591​	3.066​	43.815​
Sibling bullying (victims)​	46.470	1​	< 0.001	12.915​	6.189​	26.950​

Dependent variable: sibling bullying (bullies), adjusted analyzes based on binary logistic regression models including sex, number of siblings, parental education, parental marital status, bullies in peer bullying, physical abuse, and domestic violence as covariates

Table 4.

Factor associated with depression

Variables​	Wald​	df​	p-value​	OR​	95% CL of adjusted OR​
					Lower​	Upper​
Female	13.899​	1​	< 0.001	2.586​	1.569	4.261​
Physical abuse	4.304	1	0.038	9.502	1.133	79.709
Domestic violence	7.234​	1​	0.007	3.441	1.398​	8.468
Sibling bullying (victims)	7.165	1​	0.007​	2.082​	1.217​	3.561

Dependent variable: depression, adjusted analyzes based on binary logistic regression models including number of siblings, parental education, parental marital status, peer bullying, cyberbullying, sibling bullying (bullies), and low self-esteem as covariates​

Results

Demographic characteristics of study participants

In total, 352 study participants had at least one sibling and were finally enrolled in this study. There were 245 (69.6%) male and 107 (30.4%) female adolescents. Half of the participants were in the eighth grade (age 13–14 years). Two hundred and thirty-three participants (66.2%) had one sibling, 94 (26.7%) had two siblings, 19 (5.4%) had three siblings, and 6 (1.7%) had more than three siblings. Paternal and maternal education was mainly below the bachelor’s degree, accounting for 61.6% and 51.2%, respectively. Other demographic characteristics of the study participants are shown in Table 1.

The prevalence of sibling bullying (Hypothesis 1)

Regarding the bullying by siblings reported by study participants, 92 (26.1%) were victims, 49 (13.9%) were bullies, and 35 (9.9%) were both bullies and victims. The most common form of sibling bullying for both victims and bullies was verbal bullying, especially names calling, making fun of, or teasing in a hurtful way. Other types of sibling bullying for those who were victimized or bullied their siblings are illustrated in eTables 1 and 2.

Peer bullying, cyberbullying, physical abuse by parents, and domestic violence

In addition to bullying by siblings, 36 (10.2%) and 25 (7.1%) participants were also victimized by peer bullying and cyberbullying, respectively. On the other hand, 22 (6.3%) and 13 (3.7%) participants were perpetrators of peer bullying and cyberbullying, respectively. Additionally, 11 (3.1%) participants reported that their parents physically abused them, while 29 (8.2%) of the participants noted that there was domestic violence in the past 6 months.

Depression and self-esteem

Of 352 participants, 120 (34.1%) reported higher scores at or above the depression cut-off point. Regarding self-esteem, participants rated their self-esteem with a median of 25 (IQR 24–26), placing most of them (344, 97.7%) in the moderate to high self-esteem group.

Factors associated with sibling bullying (Hypothesis 2)

In univariate analyzes, those who were victims of sibling bullying were more likely to be female (40.2% vs 26.9%, $\chi$² 5.68, p = 0.017), being victims of peer bullying (29.3% vs 3.5%, $\chi$² 49.60, p < 0.001), and cyberbullying (15.2% vs 4.2%, $\chi$² 12.43, p < 0.001). Furthermore, this group of participants was also physically abused by their parents (9.8% vs 0.8%, $\chi$² 18.24, p < 0.001) and had domestic violence in their homes (20.7% vs 3.8%, $\chi$² 25.39, p < 0.001). As expected, those who were victimized by their siblings tended to also bully their siblings (38.0%) and vice versa (71.4%, $\chi$² 60.49, p < 0.001).

Similarly, individuals who bullied their siblings were more likely to be perpetrators of peer bullying and cyberbullying, were physically abused by their parents, and had domestic violence in their households. However, sibling bullying was not significantly associated with the number of siblings, parental education, parental marital status, and the self-esteem of the participants.

According to the associations among sibling bullying, demographic characteristics, peer and cyberbullying, physical abuse, and domestic violence mentioned above, the factors associated with being victims of sibling bullying in the final binary logistic regression model included female sex, being victims of peer bullying, domestic violence, and being bullies in sibling bullying, which increased odds 2.46, 12.99, 4.48, and 9.81 times, respectively (Table 2). Furthermore, cyberbullies and victims of sibling bullying were finally associated with an increased risk of being perpetrators of sibling bullying adjusted for sex, number of siblings, parental education, parental marital status, bullies in peer bullying, physical abuse, and domestic violence (Table 3).

Sibling bullying, depression, and self-esteem (Hypothesis 3)

In univariate analyzes, those with higher scores of depressive symptoms were more likely to be of the female sex (45.0% vs 22.8%, $\chi$² 18.35, p < 0.001), being victims of sibling bullying (40.8% vs 18.5%, $\chi$² 20.37, p < 0.001), and peer bullying (16.7% vs 6.9%, $\chi$² 8.22, p = 0.004). Furthermore, individuals with depressive symptoms tended to be physically abused by their parents (8.3% vs 0.4%, $\chi$² 16.31, p < 0.001) and had domestic violence in their households (16.7% vs 3.9%, $\chi$² 17.11, p < 0.001). Furthermore, being victims of peer bullying was the only factor significantly related to the low self-esteem of the participants.

Factors that were ultimately associated with an increased risk of depression in study participants included female sex, victims of sibling bullying, physical abuse, and domestic violence adjusted for the number of siblings, parental education, parental marital status, peer bullying, cyberbullying, and bullies of sibling bullying (Table 4). Regarding self-esteem, being victims of peer bullying was the only factor associated with an increase in the risk of low self-esteem adjusted for the same covariates (eTable 3).

Discussion

To our knowledge, this is the first study to determine the prevalence of sibling bullying, factors that affect sibling bullying, and its association with self-esteem and depression in the context of Asian countries and under the COVID-19 pandemic. The prevalence of sibling bullying in this current study differed by the situation, which observed 26.1% as victims, 13.9% as bullies, and 9.9% as both bullies and victims of sibling bullying. As hypothesized, such rates of sibling bullying for both victims and bullies in this current study were comparable to previous studies without the pandemic, which reported 8–53.8% for victims and 4–40% for perpetrators of the situation [1–6, 13]. Although this study was conducted during the COVID-19 pandemic between January and February 2022, the prevalence rate of sibling bullying observed in this study contrasted with previous studies that reported a higher prevalence of sibling bullying during the pandemic [15, 16]. This finding occurred despite the fact that our participants tended to spend more time with their siblings during the Omicron variant pandemic. It is possible that they have adapted to the “new normal” after encountering the COVID-19 pandemic for almost 2 years since the first outbreak. Furthermore, most of the sibling bullying in our study was verbal bullying, similar to a previous study [1]. However, being perpetrators and victims was the most common type of sibling bullying in previous studies [1, 5, 6, 26], which differed from our study. This difference between studies may be due to differences in cultural background, underreporting, and age at enrollment, where the bully/victim trend appeared to decrease during later adolescence [5, 6].

Regarding factors that affect sibling bullying, as hypothesized, there was a strong association between victimization by siblings and perpetration of sibling bullying where either type of sibling bullying was associated with another type of sibling bullying, as also observed in the previous literature [1, 5, 26]. This association might be related to the high tendency of bully-victims in the same individuals where there was a power dynamic between siblings that can change from one to another [1]. Furthermore, this present study also showed associations between victims of sibling bullying with female sex, peer victimization as hypothesized, and domestic violence. Such associations were also observed in previous studies [1–3, 5, 7, 12, 13, 26–29]. Experiences of polyvictimization by siblings and peers, in addition to domestic violence, can put these individuals at increased risk of emotional and behavioral problems [5].

Another interesting factor that was significantly associated with perpetrating sibling bullying was bullies in cyberbullying. Although students who were involved in cyberbullying tended to also engage in bullying and victimization at school in a previous study [30], to our knowledge, the association between perpetrating sibling bullying and cyberbullying is not obviously established. The mechanism of such an association is unclear. This could be plausibly due to the fact that individuals who reported being perpetrators of cyberbullying can have risk behaviors on the Internet, the tendency of their misbehaviors, and interpersonal conflicts in various circumstances that could put them at risk of participating in cyberbullying perpetration, as observed in the context of peer bullying [30].

In terms of depression, factors associated with an increased risk of depression were female sex, victims of bullying by siblings, as predicted in our hypothesis, as well as physical abuse by parents, and domestic violence. According to previous studies, individuals who were frequently bullied by their siblings were more likely to develop depression, maladaptiveness, emotional, behavioral, internalizing and externalizing problems, as well as psychological distress, self-harm, and decreased well-being [1, 2, 5–7, 13, 28]. Furthermore, those who were bullied by their siblings, who lived in households with domestic violence, and who were also physically abused by their parents were less likely to escape such circumstances [5]. As a result, these adverse childhood experiences could potentially affect the neuroendocrine immune network that ultimately resulted in various health and mental outcomes, including depression [31–33]. Although in another study an association was observed between victims of sibling bullying and depression for both sexes [2], our study showed an association between depression and only female adolescents. However, our finding was comparable to previous studies in which internalizing problems, including depression, were more prevalent in female adolescents [34–36]. Regarding the association between sibling bullying and low self-esteem, it was not observed in this current study, as primarily hypothesized. It could be caused by a higher tendency for moderate to high self-esteem in our participants that could not demonstrate significant differences in the context of bullying by siblings. However, the association between peer bullying and low self-esteem in this present study was supported by previous literature [37, 38].

Our study has several limitations that should be mentioned. First, the main findings on associations between variables in this current study could not be interpreted as causal relationships based on the cross-sectional nature of the study. We enrolled participants based on convenient sampling so that our findings could not be generalized to other settings. Furthermore, the sample used in this study may not represent the national prevalence of sibling bullying among Thai students in this age group. Therefore, the prevalence documented in this study should not be used to infer the national prevalence of sibling bullying among Thai students. Second, data collection was based only on the participant’s report. Self-report biases should be mitigated by collecting data from other sources, including parents, other family members, and teachers, in addition to the clinical evaluation of depression. Third, depressive symptoms, self-esteem, and other associated factors may not reflect actual circumstances without the pandemic. As a result, our main findings should be interpreted with caution. Fourth, our sample had an unequal sex distribution, since each school had different male to female ratios among students. Wat Ratchabophit School had 100% male students in grades 7 to 9, while Surasak Montri School and Triam Udom Suksa Nomklao School had 55.9% and 48.8% male students, respectively. Of 352 participants, 190, 66, and 96 were from each respective school. This could potentially explain the uneven distribution of male and female students in our sample. Fifth, the 95% CIs for some of our associated factors, such as sibling bullying in Tables 2 and 3, and physical abuse in Table 4 were very wide. This was likely due to the relatively small sample size in certain subgroups, such as those who reported being victims, bullies, or experiencing physical abuse, or when the proportion of the outcome variable was low. Although the wide confidence intervals suggested a lower precision of the estimates, they did not necessarily imply that such estimates were unreliable. However, we were very confident about the reliability of our estimates and cautioned readers to interpret our results with care, as mentioned above. Furthermore, we did not find evidence of a lack of association between our predictor and outcome variables, as our estimates were statistically significant at the defined significance level. Sixth, in this present study, no clear trend in the prevalence of sibling bullying during the pandemic was observed. To fully understand potential trends, prospective longitudinal cohorts are needed, as documented in previous studies [15, 16]. Lastly, although various covariates were adjusted in our final analyzes, there were still other residual confounding factors, including child temperament, preexisting behaviors and emotional regulation, siblings’ relationships, parent–child interaction, parenting behaviors, parents’ mental health, as well as family stress that should be further considered in future studies.

In summary, sibling bullying was not uncommon in Thai young adolescents during the COVID-19 pandemic and was associated with female sex, peer bullying, domestic violence, and depression. Perpetrating cyberbullying was also related to bullies of sibling bullying. Such associations should be identified early so that preventive measures and management could be properly implemented.

Supplementary Information

Below is the link to the electronic supplementary material.

Authors' contributions

ML had substantial contributions to conception and design, data acquisition, preliminary analysis, and data interpretation, drafted the article, and finally approved the version to be published. KJ had the main responsibility in data analysis and data interpretation and finally approved the version to be published. WC made substantial contributions to the conception and design, analysis, and interpretation of data; drafted the article and revised it for important intellectual content; and finally approved the version to be published.

Availability of data and material (data transparency)

Data from this study are available from the corresponding author on reasonable request.

Code availability (software application or custom code)

Not applicable.

Declarations

Ethics approval

This study was performed in line with the principles of the Declaration of Helsinki. Approval was granted by the Institutional Review Boards of the Faculty of Medicine of Chulalongkorn University, Bangkok, Thailand (IRB No. 588/64).

Consent to participate

Parents gave their written informed consent, and participants gave their assent.

Consent for publication

Not applicable.

Competing interests

The authors declare that they have no financial or nonfinancial interests that are directly or indirectly related to the work submitted for publication to disclose.