Video Abstract
Transgender adolescents experience disproportionately high rates of dating violence and peer victimization. However, research has relied on small samples of transgender youth and has not captured victimization experiences of gender-expansive youth (who do not identify as male, female, or transgender). In the current study, we address these limitations, comparing victimization by gender.
We examined a subsample of 4464 male, female, transgender, and gender-expansive youth (1116 per group) from the 2018 Illinois Youth Survey who were frequency matched on grade, race, geographic region, and free or reduced lunch status. Prevalence of self-reported verbal, physical, and cyber peer victimization and physical and psychological dating violence was calculated. Adjusted prevalence ratios were obtained by using log-binomial regression.
The highest rates across all forms of victimization were reported among transgender (15.6%–51.6%) and gender-expansive (13.2%–41.4%) youth. Transgender youth had a 2.09 to 2.96 times higher frequency of victimization than male youth and a 1.34 to 2.65 times higher frequency of victimization than female youth. Transgender youth also had higher frequencies of specific forms of victimization than gender-expansive youth. Gender-expansive youth had a 1.83 to 2.61 times higher frequency of victimization than male youth and 1.18 to 2.35 times higher frequencies of most forms of victimization than female youth.
Disparities in dating violence and peer victimization rates exist among transgender and gender-expansive adolescents compared with male and female youth. The distinct experiences of transgender and gender-expansive youth should be considered in school policies and violence prevention programs.
Transgender adolescents experience disproportionately high rates of dating violence and peer victimization. Research has relied on small samples and has not captured experiences of gender-expansive youth (who do not identify as male, female, or transgender).
Through matched design, creating comparable groups of gender identities according to sociodemographic characteristics, we found significant disparities in the prevalence of dating violence and peer victimization among transgender and gender-expansive adolescents compared with adolescents identifying as male or female.
Victimization within peer and dating relationships is a public health concern that impacts many adolescents and leads to an array of negative health outcomes.1 Peer victimization includes experiencing physical, verbal, or cyber forms of aggression that are unwanted and perpetrated by a peer or a group of peers.2 Forms of victimization also may occur within current or previous dating relationships, referred to as dating violence. Victimization in these contexts can increase the risk for physical injury, negative mental health symptoms, academic difficulties, self-harm, and suicide.3 Dating violence and peer victimization are an even greater public health concern for lesbian, gay, bisexual, transgender, and questioning or queer (LGBTQ) adolescents because researchers have found that LGBTQ adolescents experience higher rates of victimization compared with non-LGBTQ youth.4
To date, most researchers have examined rates of victimization by grouping all LGBTQ adolescents in analyses. However, collapsing the identities that compose LGBTQ into 1 grouping may obscure findings or lead to assumptions or misconceptions of homogeneity between experiences of sexual- and gender-minority youth.5 Sexual identity or orientation includes emotional, romantic, or sexual attraction toward other individuals, whereas gender “refers to the attitudes, feelings, and behaviors that a given culture associates with a person’s biological sex.”6 Thus, gender identity describes an individuals’ psychological sense of gender, and individuals may express their gender identity through their physical appearance or behaviors. Grouping sexual and gender identities may fail to capture the distinct experiences of youth who identify as a sexual minority, a gender minority, or both.
Research is critically needed to examine adolescent outcomes by gender identity, which includes examining cisgender, transgender, and gender-expansive individuals. Cisgender describes individuals whose gender identity is congruent with the gender typically associated with the sex assigned at birth. A transgender identity can be used to describe individuals whose gender identity or expression is not congruent with the traits culturally associated with the sex assigned at birth.7 Youth also may not identify as female, male, or transgender; the umbrella term “gender expansive” has been used to describe individuals whose gender identity or expression is beyond the purported male-female gender binary or those who do not identify with 1 specific gender.8 It is important to examine distinct experiences on the basis of these gender identities so that prevention efforts can better protect diverse adolescents.
In one study, rates of victimization by these distinct identities were examined, in which lesbian, gay, and bisexual (LGB) youth were compared with non-LGB youth and transgender youth were compared with male and female youth. In this study, the authors found that LGB youth experienced higher levels of physical and psychological dating violence compared with heterosexual youth. Additionally, a small group of transgender youth (n = 18) were compared with male and female youth; these transgender youth experienced significantly higher levels of physical (88.9%) and psychological (58.8%) forms of dating violence compared with male (35.9% physical; 44.2% psychological) and female youth (23.9% physical; 49.7% psychological).8
In other studies, authors have examined disparities in rates of victimization among transgender youth in comparison with male or female youth. In a national survey, it was found that ∼35% of transgender youth were bullied at school, compared with 15% of male-identifying and 21% of female-identifying youth. Similar disparities were found for electronic bullying (30% of transgender, 10% of male, and 19% of female youth) and physical dating violence (26.4% of transgender, 5.8% of male, and 8.7% of female youth).9 In another study, the authors found that transgender youth had significantly higher levels of peer victimization and dating violence compared with cisgender youth.4 Although some research has revealed disparities for transgender youth, researchers have yet to capture the experiences of gender-expansive adolescents.
The handful of studies in which authors have examined the prevalence of dating violence and peer victimization by gender identity have revealed a significant disparity: transgender youth are at a significantly higher risk than male or female youth for peer victimization and dating violence. However, to our knowledge, there have been no studies in which researchers have compared the prevalence of victimization using a statistical methodology that allows for a balanced comparison. In most studies, researchers have also compared a small number of transgender youth (∼1% of the sample) with larger samples of male or female youth, making interpretations difficult. Research is also needed to examine victimization among gender-expansive youth because most literature has relied on male, female, or transgender samples.10,11
In the current study, we aimed to address these limitations, examining the prevalence of dating violence and peer victimization among adolescents who identified as transgender, female, or male as well as youth who did not identify as these categories, here referred to as gender expansive. In this study, we also used matching methods to create a balanced sample from a large statewide survey, making it comparable across gender identities. It was hypothesized that transgender and gender-expansive youth would experience significantly higher levels of dating violence and peer victimization in comparison with youth who identified as male and female.
Methods
Study Design and Procedures
In the current study, we used secondary data from the cross-sectional 2018 Illinois Youth Survey (IYS)12 to compare the prevalence of peer victimization and dating violence by gender identity, matched by selected sociodemographic characteristics. The IYS is a self-report survey administered biennially in schools and collects information about health, social, and behavioral indicators. The survey is available to all public and private schools in Illinois. The survey is anonymous and voluntary and is administered online or on paper during the spring. Caregivers are notified about the IYS through an informational letter and may give passive parental consent (ie, parents or guardians return the form if they do not want their child to participate). All study procedures were approved by a university institutional review board.
Participants
More than 230 000 youth (grades 8–12) in 935 schools across 98 counties participated in the 2018 IYS. Youth with passive parental consent who answered, “I was very honest,” to the question “How honest were you in filling out this survey?” were included (N = 199 743). Youth self-identified as female (n = 100 117 or 50.22%), male (n = 95 575 or 47.94%), or transgender (n = 1204 or 0.60%) or selected “I do not identify as female, male, or transgender” (n = 2478 or 1.24%). Given the imbalanced proportions among gender identities, frequency matching was performed in the selection of a subsample on the basis of 4 variables (grade, free or reduced lunch, race, and geographic region) to create identical distributions of these variables across all gender identities with equal sample sizes. We used these variables as our matching criteria because the IYS uses these same variables to create a representative sample.12 We obtained a final sample of 4464, which consisted of 1116 youth from each gender group (ie, male, female, transgender, and gender-expansive youth). The sample size had >80% power (α = .05) to detect an absolute difference of 5% if the prevalence of victimization was 20%. Transgender youth were the smallest gender-identity group in the IYS (n = 1204), and 1116 (93%) transgender youth were included in the current study.
Measures
Students were asked questions about peer victimization in the past 12 months, including verbal, physical, and cyber forms. The question began, “Has another student at school…,” and possible answers were as follows: (1) “bullied you by calling you names?” (2) “bullied you by hitting, punching, kicking, or pushing you?” and (3) “bullied, harassed, or spread rumors about you on the Internet or through text messages?” Students responded “yes” or “no” to these questions. Students were also asked questions about physical and psychological dating violence in the past 12 months. These items included the following: (1) “Have you been slapped, kicked, punched, hit, or threatened in a dating relationship?” and (2) “Has someone put you down or tried to control you in a dating relationship?” Students responded “yes,” “no,” or “I have not begun to date.” Data were analyzed for those who responded “yes” or “no.”
Data Analysis
The distribution of the sample according to grade, free or reduced lunch, race, and geographic region was obtained by using an unweighted analysis. Because 93% of the transgender youth in the IYS were included, this distribution may be considered representative of the unweighted transgender youth in the IYS. Assuming the other gender-identity categories followed this distribution, the prevalence and 95% confidence interval (CI) of peer victimization and dating violence were determined. Thus, the prevalence obtained for other groups by using the matched sample can be considered standardized to the Illinois youth transgender population.13 χ2 tests were conducted to determine the association between gender and victimization (α = .05). Finally, a log-binomial regression model was conducted to assess the relative risk of peer and dating violence victimization between gender identities after adjusting for grade, free or reduced lunch, race, and geographic region. The prevalence ratio, along with the 95% CIs, was calculated. All analyses were performed in SAS version 9.4 (SAS Institute, Inc, Cary, NC).14
Results
In the matched data set, slightly more than half of the youth identified as white (56.81%) and 40.92% of students reported free or reduced-price lunch at school. See Table 1 for descriptive information about grade and geographic residence.
Demographic Statistics (N = 4464)
. | n . | % . |
---|---|---|
Gender identity | ||
Female | 1116 | 25 |
Male | 1116 | 25 |
Transgender | 1116 | 25 |
Gender expansive (ie, do not identify as female, male, or transgender) | 1116 | 25 |
Grade | ||
Eighth | 1188 | 26.61 |
Ninth | 400 | 8.96 |
10th | 1348 | 30.2 |
11th | 408 | 9.14 |
12th | 1120 | 25.09 |
Race | ||
White | 2536 | 56.81 |
Black or African American | 248 | 5.56 |
Hispanic | 476 | 10.66 |
Asian American | 184 | 4.12 |
American Indian | 52 | 1.16 |
Multiracial | 784 | 17.56 |
Other | 144 | 3.23 |
Missing | 40 | 0.9 |
Geographic region of residencea | ||
Suburban Chicago | 2812 | 62.99 |
Chicago | 140 | 3.14 |
Other urban or suburban | 1000 | 22.4 |
Rural | 512 | 11.47 |
Received free or reduced-price lunch | ||
Free lunch or reduced-price lunch | 1812 | 40.92 |
Neither | 2616 | 59.08 |
. | n . | % . |
---|---|---|
Gender identity | ||
Female | 1116 | 25 |
Male | 1116 | 25 |
Transgender | 1116 | 25 |
Gender expansive (ie, do not identify as female, male, or transgender) | 1116 | 25 |
Grade | ||
Eighth | 1188 | 26.61 |
Ninth | 400 | 8.96 |
10th | 1348 | 30.2 |
11th | 408 | 9.14 |
12th | 1120 | 25.09 |
Race | ||
White | 2536 | 56.81 |
Black or African American | 248 | 5.56 |
Hispanic | 476 | 10.66 |
Asian American | 184 | 4.12 |
American Indian | 52 | 1.16 |
Multiracial | 784 | 17.56 |
Other | 144 | 3.23 |
Missing | 40 | 0.9 |
Geographic region of residencea | ||
Suburban Chicago | 2812 | 62.99 |
Chicago | 140 | 3.14 |
Other urban or suburban | 1000 | 22.4 |
Rural | 512 | 11.47 |
Received free or reduced-price lunch | ||
Free lunch or reduced-price lunch | 1812 | 40.92 |
Neither | 2616 | 59.08 |
These geographic types were based on the Illinois State Board of Education’s county and census designations.
Peer Victimization by Gender
Assuming the gender-identity groups had identical distribution of the sociodemographic characteristics used for matching, the prevalence and 95% CIs of victimization by gender are shown in Fig 1. The highest rates of peer victimization of all forms were reported among transgender youth (51.61% verbal, 22.07% physical, and 36.29% cyber victimization), followed by gender-expansive youth (41.43% verbal, 19.44% physical, and 31.89% cyber victimization). Verbal and cyber peer victimization was also higher in female youth than male youth. Physical peer victimization was higher in male youth than female youth. Comparisons of verbal (χ2 = 230.42), physical (χ2 = 112.70), and cyber victimization (χ2 = 177.53) were all significantly different by gender (degrees of freedom = 3; P < .001).
Prevalence of peer victimization by gender identity (verbal peer victimization, n = 4242; physical peer victimization, n = 4212; cyber peer victimization, n = 4217). Error bars reveal 95% CIs.
Prevalence of peer victimization by gender identity (verbal peer victimization, n = 4242; physical peer victimization, n = 4212; cyber peer victimization, n = 4217). Error bars reveal 95% CIs.
Adjusted for the matched variables, transgender youth faced 2.09 to 2.96 times more peer victimization (across types of peer victimization) compared with male youth and 1.34 to 2.65 times more peer victimization compared with female youth. Transgender youth also faced 1.21 and 1.14 times more verbal and cyber forms of peer victimization, respectively, compared with gender-expansive youth. Additionally, gender-expansive youth experienced 1.83 to 2.61 times more peer victimization compared with male youth and 1.18 to 2.35 times more peer victimization compared with female youth. For all prevalence ratios, see Table 2.
Adjusted Prevalence Ratios of Dating Violence and Peer Victimization by Gender Identity
Variable . | Prevalence Ratio (95% CI) . | ||||
---|---|---|---|---|---|
Transgender Versus Femalea Youth . | Transgender Versus Malea Youth . | Transgender Versus Gender-Expansivea Youth . | Gender-Expansive Versus Femalea Youth . | Gender-Expansive Versus Malea Youth . | |
PV | |||||
Verbal PV | 1.70* (1.53–1.90) | 2.21* (1.95–2.50) | 1.21* (1.10–1.32) | 1.41* (1.25–1.58) | 1.83* (1.61–2.09) |
Physical PV | 2.65* (2.11–3.34) | 2.09* (1.69–2.57) | 1.13 (0.96–1.34) | 2.35* (1.85–2.97) | 1.84* (1.49–2.28) |
Cyber PV | 1.34* (1.18–1.51) | 2.96* (2.47–3.55) | 1.14* (1.01–1.28) | 1.18* (1.03–1.34) | 2.61* (2.17–3.14) |
DVV | |||||
Physical DVV | 2.10* (1.57–2.81) | 2.21* (1.64–2.98) | 1.19 (0.93–1.51) | 1.77* (1.30–2.41) | 1.86* (1.36–2.55) |
Psychological DVV | 1.49* (1.22–1.82) | 2.91* (2.23–3.79) | 1.25* (1.04–1.51) | 1.19 (0.96–1.47) | 2.32* (1.76–3.06) |
Variable . | Prevalence Ratio (95% CI) . | ||||
---|---|---|---|---|---|
Transgender Versus Femalea Youth . | Transgender Versus Malea Youth . | Transgender Versus Gender-Expansivea Youth . | Gender-Expansive Versus Femalea Youth . | Gender-Expansive Versus Malea Youth . | |
PV | |||||
Verbal PV | 1.70* (1.53–1.90) | 2.21* (1.95–2.50) | 1.21* (1.10–1.32) | 1.41* (1.25–1.58) | 1.83* (1.61–2.09) |
Physical PV | 2.65* (2.11–3.34) | 2.09* (1.69–2.57) | 1.13 (0.96–1.34) | 2.35* (1.85–2.97) | 1.84* (1.49–2.28) |
Cyber PV | 1.34* (1.18–1.51) | 2.96* (2.47–3.55) | 1.14* (1.01–1.28) | 1.18* (1.03–1.34) | 2.61* (2.17–3.14) |
DVV | |||||
Physical DVV | 2.10* (1.57–2.81) | 2.21* (1.64–2.98) | 1.19 (0.93–1.51) | 1.77* (1.30–2.41) | 1.86* (1.36–2.55) |
Psychological DVV | 1.49* (1.22–1.82) | 2.91* (2.23–3.79) | 1.25* (1.04–1.51) | 1.19 (0.96–1.47) | 2.32* (1.76–3.06) |
Prevalence ratios include the 95% CIs. All findings are adjusted for sociodemographic characteristics (grade, race, free or reduced lunch, and geographic region). Sample sizes were as follows: verbal PV, n = 4242; physical PV, n = 4212; cyber PV, n = 4217; physical DDV, n = 3091; and psychological DVV, n = 2337. DVV, dating violence victimization; PV, peer victimization.
Reference group.
P < .05.
Dating Violence Victimization by Gender
As shown in Fig 2, the highest rates of dating violence victimization were reported among transgender youth (15.64% physical and 36.39% psychological victimization), followed by gender-expansive youth (13.15% physical and 23.89% psychological victimization). Female youth reported higher levels of psychological dating violence than male youth. Comparisons of physical (χ2 = 43.17) and psychological (χ2 = 73.78) dating violence were all significantly different by gender (degrees of freedom = 3; P < .001).
Prevalence of dating violence victimization by gender identity (physical dating violence victimization, n = 3091; psychological dating violence victimization, n = 2337). Dating violence victimization was assessed among students who had begun to date. Error bars reveal 95% CIs.
Prevalence of dating violence victimization by gender identity (physical dating violence victimization, n = 3091; psychological dating violence victimization, n = 2337). Dating violence victimization was assessed among students who had begun to date. Error bars reveal 95% CIs.
Adjusted for the matched variables, transgender youth experienced 2.21 to 2.91 times more dating violence compared with male youth and 1.49 to 2.10 times more dating violence compared with female youth. Transgender youth also experienced 1.25 times more psychological dating violence than gender-expansive youth. Lastly, gender-expansive youth experienced 1.86 to 2.32 times more dating violence than male youth and 1.77 times higher prevalence of physical dating violence than female youth (Table 2).
Discussion
Although dating violence and peer victimization are significant public health concerns, research was underdeveloped in examining victimization among transgender and gender-expansive youth. In the current study, we addressed this critical gap by comparing forms of victimization among a large sample of male, female, transgender, and gender-expansive youth. Transgender youth reported the highest levels of victimization, followed by gender-expansive youth. These results highlight disparities in victimization experiences by diverse gender identities.
Disparities in Victimization
Slightly more than half of transgender youth reported verbal peer victimization, 1 in 3 transgender youth reported cyber victimization, and ∼1 in 3 transgender youth experienced psychological dating violence. Current findings are not surprising given previous research suggesting elevated rates.4,9,10 However, in the current study, we confirmed these disparate rates with a large sample using matched gender identities, which allowed for more accurate comparisons. Additionally, in the current study, we were able to present prevalence rates for a group of adolescents largely missing from the victimization literature, gender-expansive youth, who also reported significantly higher levels of victimization than male and female youth.
In the current study, we also found that transgender youth reported higher levels of victimization experiences than gender-expansive youth. Thus, although both groups of youth had higher rates of victimization than male and female adolescents, transgender youth reported the highest. Future researchers should consider examining what factors may explain different rates between these 2 groups, such as increased visibility of transgender and gender-expansive identities, prevailing stigma and discrimination toward noncisgender identities, and lack of supportive policies and practices. Finally, although not a primary study aim, female youth, compared with male youth, also reported higher rates of verbal and cyber peer victimization, as well as psychological dating violence, which is similar to national survey findings.15
Limitations
Despite this study’s strengths and novel findings, it also has limitations. First, although we used matching to achieve comparability of gender identities across sociodemographic characteristics, for the subsample, we used a small fraction of available observations from the IYS. This led to a loss of precision of estimates that could have been prevented if the total IYS sample were used and regression analyses controlled for confounding variables. However, we decided to use matching to achieve less model dependence in causal inference that accompanies selection of the right model in regression analysis of observational studies16 and simpler interpretation of prevalence ratios.13 Even with the reduced sample size, this study had sufficient power to detect differences in prevalence of victimization forms that we considered clinically important.
Second, we used cross-sectional data; thus, no questions could be asked about how victimization may vary over time. Third, the 5 screening questions for victimization relied on self-report with a limited response (yes or no), not capturing the frequency, severity, or longevity of victimization experiences nor capturing other experiences with victimization that may differ by gender (eg, sexual victimization, stalking).17 Fourth, because existing data were used, we did not design the question asking youth to self-report their gender identity. As such, the gender-identity response items were not more numerous or specific (eg, transgender male, transgender female, agender, a listed “gender-expansive” option). Transgender is a broad term, often used as an adjective rather than a particular gender identity, and more specific gender identities could have been gathered with a 2-step approach (asking first if someone identifies as transgender and then, asking if they identify as male, female, or another identity) or by allowing participants to select all that apply.5 We were also unable to assess if adolescents who identified as male and female were cisgender.
Finally, in the current study, we labeled participants who selected “I do not identify as male, female, or transgender” as gender-expansive youth. Labeling youth’s identities for them is not to be taken lightly. Gender expansive is considered a more inclusive term than gender nonconforming, and it has been used to include individuals who identify as gender nonbinary, genderqueer, gender-fluid, agender, or gender diverse.18 However, more research is needed to understand the most inclusive ways to assess for gender identity in surveillance surveys and research.19 For example, we were unable to necessarily capture the experiences of gender-fluid youth. “Gender-fluid” describes an individual who does not consistently identify with 1 gender and may identify differently on a day-to-day basis.20 Although “gender expansive” may include individuals who identify as gender-fluid, we had no way of assessing changes in gender identity across time or asking participants if they identified as gender-fluid. Because surveillance surveys are evolving to specify more inclusive gender categories,9 future scholars are urged to consider the nuances in the measurement of gender.20
Public Health Implications
Although an increasing number of schools have antibullying policies that include protections based on sexual or gender identity, LGBTQ students still report high levels of victimization. However, the addition of LGBTQ-related school resources, such as delivering LGBTQ-inclusive curricula, is associated with enhanced feelings of safety and connectedness and hearing fewer negative remarks related to gender.21 These policies also decreased the likelihood that students were required to use bathrooms that matched their assigned sex and wear clothing incongruent with their gender identity or expression.22 These policies can also support youth in using pronouns reflective of their gender identity at school,11 and antitransphobic education for students, teachers, and administration is necessary to further enhance the effectiveness of these policies.23 More research is necessary to assess the components and ways in which policies could reduce victimization and enhance safety and connectedness among transgender and gender-expansive youth.
Specifically within Illinois, the bullying prevention statue explicitly prohibits bullying on the basis of gender-related identity or expression.24 However, a 2020 governor-appointed task force report emphasized the need for more action and recommendations to improve school safety for transgender and gender-expansive students (eg, gender support coordinators; mandatory teacher trainings).25 In 2019, Illinois’ governor also signed the Inclusion Curriculum Law, which requires public school history curricula to include the contributions of LGBTQ people.26
In addition to policy changes, the distinct needs and experiences of transgender and gender-expansive youth need to be considered in violence prevention programming, as researchers have highlighted the overall lack of focus on sexual- and gender-minority students in programming.27,28
In this study, our use of a large statewide data set with matched subsamples for comparisons fortifies our understanding that transgender and gender-expansive adolescents are at increased risk for experiencing victimization from peers and dating partners. Future researchers should elucidate individual- and school-level risk and protective factors that influence victimization experiences of gender-diverse youth. Gender-specific forms of victimization or victimization that may result because of one’s gender identity or expression has also been examined in studies10,11,29 ; thus, researchers are urged to include these forms of victimization in future work. Finally, researchers should also consider the intersectionality of gender with other identities, such as race and ethnicity, because transgender youth who are a racial or ethnic minority may be at a greater risk for violence.30 With the current study, we provide a foundation for this future research, as well as ideas for policy and program development, highlighting significant disparities in peer victimization and dating violence reported by transgender and gender-expansive youth.
Acknowledgments
We thank the Center for Prevention Research and Development at the School of Social Work (University of Illinois at Urbana-Champaign) for providing us with the IYS data. We also thank Dr Jesus Natividad Sarol Jr, who consulted with the team for the statistical analyses. We dedicate this work to the youth who participated in the 2018 IYS.
Dr Garthe conceptualized and designed the study, drafted the initial manuscript, and reviewed and revised the manuscript; Ms Kaur conducted the data analyses, drafted sections of the initial manuscript, and reviewed and revised the manuscript; Ms Rieger, Ms Blackburn, and Ms Kim assisted with the literature review, drafted tables, drafted sections of the manuscript, and reviewed and revised the manuscript; Dr Goffnett critically reviewed the manuscript and provided revisions; and all authors approved the final manuscript as submitted.
FUNDING: No external funding was provided for this article. Data for this study were provided by the Center for Prevention Research and Development, a unit within the School of Social Work at the University of Illinois at Urbana-Champaign. Data were collected (award 43CWZ03292) from the Illinois Department of Human Services. The opinions in this article, however, reflect those of the authors and do not reflect official positions of the Center for Prevention Research and Development or the funding source.
References
Competing Interests
POTENTIAL CONFLICT OF INTEREST: The authors have indicated they have no potential conflicts of interest to disclose.
FINANCIAL DISCLOSURE: The authors have indicated they have no financial relationships relevant to this article to disclose.