Skip to main content
Browse Subject Areas

Click through the PLOS taxonomy to find articles in your field.

For more information about PLOS Subject Areas, click here.

  • Loading metrics

Asian-white disparities in obstetric anal sphincter injury: Protocol for a systematic review and meta-analysis

  • Meejin Park,

    Roles Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Project administration, Validation, Visualization, Writing – original draft, Writing – review & editing

    Affiliation Faculty of Health Sciences, Department of Global Health, McMaster University, Hamilton, ON, Canada

  • Susitha Wanigaratne,

    Roles Investigation, Methodology, Writing – review & editing

    Affiliation Sick Kids Research Institute, Edwin S.H. Leong Centre for Healthy Children, Toronto, ON, Canada

  • Rohan D’Souza,

    Roles Investigation, Methodology, Writing – review & editing

    Affiliations Faculty of Health Science, Department of Obstetrics and Gynecology, McMaster University, Hamilton, ON, Canada, Faculty of Health Sciences, Department of Health Research Methods, Evidence and Impact, McMaster University, Hamilton, ON, Canada

  • Roxana Geoffrion,

    Roles Investigation, Methodology, Writing – review & editing

    Affiliation Department of Obstetrics and Gynaecology, University of British Columbia, Vancouver, BC, Canada

  • Sarah A. Williams,

    Roles Investigation, Methodology, Writing – review & editing

    Affiliation Department of Anthropology, Brown University, Providence, RI, United States of America

  • Giulia M. Muraca

    Roles Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Project administration, Resources, Supervision, Validation, Visualization, Writing – review & editing

    Affiliations Faculty of Health Science, Department of Obstetrics and Gynecology, McMaster University, Hamilton, ON, Canada, Department of Obstetrics and Gynaecology, University of British Columbia, Vancouver, BC, Canada, Department of Medicine, Clinical Epidemiology Division, Solna, Karolinska Institutet, Stockholm, Sweden



Obstetric anal sphincter injury (OASI) describes severe injury to the perineum and perineum and perianal muscles following birth and occurs in 4.4% to 6.0% of vaginal births in Canada. Studies from high-income countries have identified an increased risk of OASI in individuals who identify as Asian race versus those who identify as white. This protocol outlines a systematic review and meta-analysis which aims to determine the incidence of OASI in individuals living in high-income countries who identify as Asian versus those of white race/ethnicity. We hypothesize that the pooled incidence of OASI will be higher in Asian versus white birthing individuals.


We will search MEDLINE, OVID, Embase, Emcare and Cochrane databases from inception to 2022 for observational studies using keywords and controlled vocabulary terms related to race, ethnicity and OASI. Two reviewers will follow the Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA) guidelines and Meta-analysis of Observational Studies (MOOSE) recommendations. Meta-analysis will be performed using RevMan for dichotomous data using the random effects model and the odds ratio (OR) as effect measure with a 95% confidence interval (CI). Subgroup analysis will be performed based on Asian subgroups (e.g., South Asian, Filipino, Chinese, Japanese individuals). Study quality assessment will be performed using The Joanna Briggs Institute Critical Appraisal tools.


The systematic review and meta-analysis that this protocol outlines will synthesize the extant literature to better estimate the rates of OASI in Asian and white populations in non-Asian, high-income settings and the relative risk of OASI between these two groups. This systematic summary of the evidence will inform the discrepancy in health outcomes experienced by Asian and white birthing individuals. If these findings suggest a disproportionate burden among Asians, they will be used to advocate for future studies to explore the causal mechanisms underlying this relationship, such as differential care provision, barriers to accessing care, and social and institutional racism. Ultimately, the findings of this review can be used to frame obstetric care guidelines and inform healthcare practices to ensure care that is equitable and accessible to diverse populations.


Racial and ethnic inequities are pervasive in maternal health and are a major source of health disparities in many settings. For example, maternal mortality rates persistently highlight racial disparities in non-Asian, high-income countries such as the United States (US) and the United Kingdom [1,2]. Studies of composite severe maternal morbidity across racial groups in Europe, Australia, and North America have shown similar trends [1,2]. However, the relationship between race/ethnicity and specific causes of maternal morbidities, such as obstetric trauma, is not yet understood.

Obstetric trauma describes severe injury to the perineum, pelvic organs, and supporting myofascial pelvic structures following birth and occurs in 4.4% to 6.0% of vaginal births in Canada [3]. Recent evidence has shown that this rate has been increasing in Canada but reasons for this trend remain speculative [4]. Obstetric trauma contributes to short-term morbidity as well as long-term, life-changing complications such as mental health morbidity, female sexual dysfunction, pain and an increase in most pelvic floor disorders including anal incontinence [510].

Evidence is accumulating on the independent association between race/ethnicity and obstetric anal sphincter injury (OASI) in non-Asian, high-income countries such as Australia, Canada, Norway, and the US [1118]. Although many of these studies have observed higher rates of obstetric trauma among racial and ethnic minorities, these analyses have been limited by poorly defined or inconsistent racial categories, limited sample sizes, and a lack of generalizability. However, a systematic review [19] conducted in 2012 found that rates of OASI among Asian individuals residing in Asian countries were similar to those observed in white, high-income populations. By contrast, those of Asian ethnicity had up to four-fold higher rates of OASI compared with white individuals in Western countries. In the years following this narrative review, researchers’ understanding of the quality-of-life impairing long-term consequences of OASI have evolved and resulted in an intensified interest in understanding the distribution of these injuries and their risk factors. Several additions to the literature on this topic have since emerged. Thus, an updated review that includes additional studies since 2012 and synthesizes the evidence on the relationship between Asian race/ethnicity and OASI using meta-analysis is warranted.

The systematic review and meta-analysis outlined in this protocol will include the up-to-date published studies on this topic and aims to summarize these data using meta-analysis to provide pooled estimates of the association between Asian race and OASI, and investigate any heterogeneity in these associations among different Asian racial/ethnic subgroups. We hypothesize that the pooled incidence of OASI will be higher in Asian versus white individuals.

Materials and methods

Study design

This systematic review has been registered in the International Prospective Register of Systematic Reviews (PROSPERO; registration no. CRD42022379141). Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA) guidelines [20] and Meta-analysis of Observational Studies (MOOSE) recommendations [21] were used to guide the protocol (S1 File).

Eligibility criteria

We will search MEDLINE, OVID, Embase, Emcare and Cochrane databases from inception to 2022 for observational studies using keywords and controlled vocabulary terms related to race, ethnicity and OASI. All observational studies, including cross-sectional, case-control, and cohort will be included. Case reports, case series, literature reviews, conference abstracts and gray literature will be excluded from the review. No restrictions based on language will be applied. Studies that do not provide sufficient information to calculate effect size will be excluded.

Studies with all criteria satisfying the PECOS framework will be included in the review.

  • Population: Individuals with live or stillbirth in non-Asian, high-income countries.
  • Exposure: Asian race/ethnicity will be defined using the outline by the United Nations (UN) [22]. Studies that aggregated individuals of Asian race with other racial groups will not be included. Due to the absence of standard definitions, misuses of the terms ‘ethnicity’, ‘race’, and ‘ancestry’ have been reported [15,2326]. In this study, we understand the term ‘race’ to reflect socio-political inequalities, which are often based on “perceived physical differences” such as skin and eye colour [18,23,26]. Ethnicity is defined by cultural factors including language and nationality [26]. For example, there are linguistic, cultural and historical variations within Asian populations [27]. However, discrimination based on a patient’s linguistic differences and misinformed cultural assumptions persists [27].
  • Comparators: Studies will be included if they compared outcomes in Asian individuals with those in white individuals. The white population serves as a comparison group as they are the predominate ethnic group in non-Asian, high-income countries and because they are not affected by the institutional racism that underlies racial inequities in health. Studies that aggregated white individuals with other racial groups will be excluded.
  • Outcome: Obstetric anal sphincter injury (3rd or 4th degree perineal laceration). Third-degree lacerations involve a partial or complete disruption of the internal and/or external anal sphincter. Fourth-degree lacerations involve the disruption of the anal mucosa in addition to laceration of the external and internal anal sphincter [28]. This is the established definition of OASI adopted by the Society for Obstetricians and Gynaecologists of Canada [29], the American College of Obstetricians and Gynecologists [30], and the World Health Organization and the International Consultation on Incontinence [31].

Search strategy

We will systematically search MEDLINE, OVID, Embase, Emcare, and the Cochrane electronic database from inception to the date of our literature search for observational studies comparing the risk of OASI between Asian and white individuals. We will use keywords and controlled vocabulary terms related to race, ethnicity and OASI, including “race,” “ethnicity,” “Asian” “obstetric anal sphincter injury” and “severe perineal lacerations.” Details of the search strategy are provided in S2 File. Additional papers will be included through hand searching of references of included papers.

Screening procedure

Two reviewers (MP & GMM) will independently screen titles and abstracts of the articles retrieved from the search for study eligibility. Disagreements will be resolved through discussions with both reviewers. If disagreements persist, conflicts will be raised with the wider study team until consensus is reached. Articles deemed potentially eligible will be carried forward for full-text screening by the two reviewers independently using Covidence ( to select the final articles using the predefined inclusion and exclusion criteria.

Data extraction

Two reviewers (MP & GMM) will extract study characteristics including last name of first author, year of publication, country, study design, sample size, overall incidence of OASI, race/ethnicity groups included, Asian subgroups examined, method used to specify race/ethnicity, method used to identify OASI and confounders included in adjusted models (e.g., forceps or vacuum delivery, episiotomy, maternal age, duration of labour, and macrosomic infant). The number of events, number of Asian and white individuals, unadjusted and adjusted odds ratios (OR) as well as 95% confidence intervals (CI) from each study will also be included.

Risk of bias assessment

Two reviewers (MP, GMM) will independently assess the methodological quality of studies using the Joanna Briggs Institute Critical Appraisal tools, which evaluates risk of bias using a checklist of ten items. These items will be answered with “yes,” “no,” “maybe” or “not applicable.” A numerical score will then be calculated (yes = 1, no/maybe/not applicable = 0). A total score greater than 7 will be considered indicative of low risk of bias, while scores between 4 and 7 will be classified as medium risk, and those between 1 and 3 will be categorized as high risk of bias. Reviewers will resolve any disagreement in bias assessment by discussion. Publication bias will be assessed by constructing funnel plots.

Data synthesis and analysis

Meta-analysis will be performed using RevMan 5.4 for dichotomous data using the random effects model and the odds ratio (OR) as an effect measure with a 95% confidence interval (CI). We will calculate the unadjusted OR from raw data using the Mantel-Haenszel method. We will also use separate random-effects models to pool the reported unadjusted and adjusted ORs using the inverse variance method. This will enable us to 1) include studies that report unadjusted ORs but do not provide the raw data into a pooled OR estimate of OASI in Asian compared with white individuals and 2) pool adjusted estimates of OASI in Asian compared with white individuals. We will assess the heterogeneity of studies using the I2 statistic. We will consider heterogeneity significant when the I2 is greater than 50%, following Cochrane Collaboration recommendations.

Subgroup analyses will be performed using studies that compare OASI in specific Asian subgroups (e.g., South Asian, Filipino, Chinese, Japanese individuals) compared with white individuals, by study design (hospital-based versus population-based) and by mode of delivery (operative versus spontaneous vaginal delivery) depending on the number of studies that would allow for sub-analyses.

We will also conduct subgroup analyses excluding studies deemed to have a high risk of bias. In the event that there is high heterogeneity and if there are sufficient studies eligible for synthesis, we will conduct meta-regression to explore the source of heterogeneity among the included studies.


Obstetric trauma is an area of increasing global health importance, yet its differential burden in specific racial/ethnic groups remains understudied. This is of particular concern since a secular increase in the rate of OASI has been evidenced in several high-income countries in recent years [4,3237] and the impact of this increase on the Asian diaspora is unknown. For example, Asian Americans in the United States have increased in population size by 70% between 2000 and 2020 [38]. Despite this, the health of Asian Americans remains a largely understudied population; only 0.17% of the Institutes of Health (NIH) funding between 1992–2018 was allocated to the subject [38].

Differential access to health care among racial and ethnic minority populations impacts the health outcomes of these populations in majority-white countries. Racism has been a part of medicine and everyday clinical practice for centuries, resulting in quality of life-impairing outcomes and excess morbidity and mortality among BIPOC (Black, Indigenous, and people of colour) individuals [39]. For example, the undertreatment of pain in Black individuals compared with white individuals based on the false biological belief that Black patients experience a lower sensitivity to pain, resulting in inaccurate treatment prescriptions [40].

By answering the question ‘is there an increased incidence of OASI in Asian versus white individuals’, this systematic review and meta-analysis has many strengths. First, it may confirm that studies from non-Asian, high-income countries indicate an increased risk of OASI in Asian individuals compared with white individuals while displaying lower crude rates of OASI in studies conducted in Asia. Second, it may support the need to advocate for future studies to explore causal mechanisms underlying this relationship. Additional strengths of our project are the proposed subgroup analyses (e.g., by specific Asian ethnicity, Chinese, Japanese, Indian), which has the potential to reveal heterogeneity in the relationship between specific Asian race/ethnicity and OASI. Lastly, this work will serve to advocate for more accurate collection of race-based data (e.g., use of self-report in race/ethnicity measurement) which is critical for advancing health equity. The findings of this study may inform obstetric healthcare practice guidelines on issues related to equitable and accessible care for diverse populations.

The main limitation of this protocol includes challenges in the measurement of race/ethnicity. Dichotomous categorizations of race do not capture the complexity with which race impacts maternal outcomes. We expect to find heterogeneity in the definition of Asian race as has been found in previous research on racial disparities with conventionally used race categories [41]. This can cause misleading results, as it assumes uniform effects within Asian subpopulations and dismisses specific subgroup disparities [38]. In addition, To define Asian countries, we applied a UN classification system named “Standard country or area codes for statistical use (M49)” [22]. While comprehensive, this classification scheme has limitations because there are several transcontinental countries, such as Kazakhstan, which can be identified as both Asian and European depending on historical, geographical, and cultural contexts [42,43]. This means that the geographical classification used by the UN may differ from the self-identification of race/ethnicity of study participants. We anticipate most studies will include a singular self-reported ’Asian’ category that is compared with a singular, self-reported ’white’ category. If this is realized, the meta-analysis will be carried out to take a close look at the level of heterogeneity detected.

Any amendments made to the protocol will be reflected on PROSPERO. The manuscript will be submitted to a peer-reviewed journal in the field of obstetrics and gynaecology. Presentation opportunities in research conferences will also be sought.

Supporting information

S1 File. PRISMA-P 2015 checklist.

Preferred Reporting Items for Systematic review and Meta-Analysis Protocols 2015 checklist: recommended items to address in a systematic review protocol.


S2 File. Systematic review search strategy.

Controlled vocabulary terms related to race, ethnicity and OASI.



  1. 1. Admon LK, Winkelman TNA, Zivin K, Terplan M, Mhyre JM, Dalton VK. Racial and Ethnic Disparities in the Incidence of Severe Maternal Morbidity in the United States, 2012–2015. Obstet Gynecol. 2018 Nov;132(5):1158–66. pmid:30303912
  2. 2. Holdt Somer SJ, Sinkey RG, Bryant AS. Epidemiology of racial/ethnic disparities in severe maternal morbidity and mortality. Semin Perinatol. 2017 Aug;41(5):258–65. pmid:28888263
  3. 3. Hobson S, Cassell K, Windrim R, Cargill Y. No. 381-Assisted Vaginal Birth. J Obstet Gynaecol Can JOGC J Obstet Gynecol Can JOGC. 2019 Jun;41(6):870–82.
  4. 4. Muraca GM, Lisonkova S, Skoll A, Brant R, Cundiff GW, Sabr Y, et al. Ecological association between operative vaginal delivery and obstetric and birth trauma. CMAJ. 2018 Jun 18;190(24):E734–41. pmid:29914910
  5. 5. Handa VL, Danielsen BH, Gilbert WM. Obstetric anal sphincter lacerations. Obstet Gynecol. 2001 Aug;98(2):225–30. pmid:11506837
  6. 6. Wegnelius G, Hammarström M. Complete rupture of anal sphincter in primiparas: long-term effects and subsequent delivery. Acta Obstet Gynecol Scand. 2011 Mar;90(3):258–63. pmid:21306305
  7. 7. Nilsson IEK, Åkervall S, Molin M, Milsom I, Gyhagen M. Symptoms of fecal incontinence two decades after no, one, or two obstetrical anal sphincter injuries. Am J Obstet Gynecol. 2021 Mar 1;224(3):276.e1–276.e23. pmid:32835724
  8. 8. Priddis H, Schmied V, Dahlen H. Women’s experiences following severe perineal trauma: a qualitative study. BMC Womens Health. 2014 Feb 21;14(1):32. pmid:24559056
  9. 9. Tilak M, Mann GK, Gong M, Koenig NA, Lee T, Geoffrion R. Pelvic floor healing milestones after obstetric anal sphincter injury: a prospective case control feasibility study. Int Urogynecology J. 2022 Sep 13;1–9. pmid:36098790
  10. 10. Handa VL, Blomquist JL, McDermott KC, Friedman S, Muñoz A. Pelvic floor disorders after vaginal birth: effect of episiotomy, perineal laceration, and operative birth. Obstet Gynecol. 2012 Feb;119(2 Pt 1):233–9. pmid:22227639
  11. 11. Sørbye IK, Bains S, Vangen S, Sundby J, Lindskog B, Owe KM. Obstetric anal sphincter injury by maternal origin and length of residence: a nationwide cohort study. BJOG Int J Obstet Gynaecol. 2022 Feb;129(3):423–31. pmid:34710268
  12. 12. Baghestan E, Irgens LM, Børdahl PE, Rasmussen S. Trends in risk factors for obstetric anal sphincter injuries in Norway. Obstet Gynecol. 2010 Jul;116(1):25–34. pmid:20567164
  13. 13. Goldberg J, Hyslop T, Tolosa JE, Sultana C. Racial differences in severe perineal lacerations after vaginal delivery. Am J Obstet Gynecol. 2003 Apr;188(4):1063–7. pmid:12712111
  14. 14. Guendelman S, Thornton D, Gould J, Hosang N. Obstetric complications during labor and delivery: assessing ethnic differences in California. Womens Health Issues Off Publ Jacobs Inst Womens Health. 2006;16(4):189–97. pmid:16920523
  15. 15. Hauck YL, Lewis L, Nathan EA, White C, Doherty DA. Risk factors for severe perineal trauma during vaginal childbirth: a Western Australian retrospective cohort study. Women Birth J Aust Coll Midwives. 2015 Mar;28(1):16–20. pmid:25476878
  16. 16. Hopkins LM, Caughey AB, Glidden DV, Laros RK. Racial/ethnic differences in perineal, vaginal and cervical lacerations. Am J Obstet Gynecol. 2005 Aug;193(2):455–9. pmid:16098870
  17. 17. Quist-Nelson J, Hua Parker M, Berghella V, Biba Nijjar J. Are Asian American women at higher risk of severe perineal lacerations? J Matern-Fetal Neonatal Med Off J Eur Assoc Perinat Med Fed Asia Ocean Perinat Soc Int Soc Perinat Obstet. 2017 Mar;30(5):525–8. pmid:27071715
  18. 18. Brown J, Kapurubandara S, Gibbs E, King J. The Great Divide: Country of birth as a risk factor for obstetric anal sphincter injuries. Aust N Z J Obstet Gynaecol. 2018 Feb;58(1):79–85. pmid:28776641
  19. 19. Wheeler J, Davis D, Fry M, Brodie P, Homer CSE. Is Asian ethnicity an independent risk factor for severe perineal trauma in childbirth? A systematic review of the literature. Women Birth J Aust Coll Midwives. 2012 Sep;25(3):107–13. pmid:21880563
  20. 20. Liberati A, Altman DG, Tetzlaff J, Mulrow C, Gøtzsche PC, Ioannidis JPA, et al. The PRISMA statement for reporting systematic reviews and meta-analyses of studies that evaluate healthcare interventions: explanation and elaboration. BMJ. 2009 Jul 21;339:b2700. pmid:19622552
  21. 21. Stroup DF, Berlin JA, Morton SC, Olkin I, Williamson GD, Rennie D, et al. Meta-analysis of observational studies in epidemiology: a proposal for reporting. Meta-analysis Of Observational Studies in Epidemiology (MOOSE) group. JAMA. 2000 Apr 19;283(15):2008–12. pmid:10789670
  22. 22. United Nations. Geographic Regions. [cited 2023 Feb 3]. UNSD—Methodology. Available from:
  23. 23. Anand SS. Using Ethnicity as a Classification Variable in Health Research: Perpetuating the myth of biological determinism, serving socio-political agendas, or making valuable contributions to medical sciences? Ethn Health. 1999 Nov 1;4(4):241–4. pmid:10705561
  24. 24. Ross PT, Hart-Johnson T, Santen SA, Zaidi NLB. Considerations for using race and ethnicity as quantitative variables in medical education research. Perspect Med Educ. 2020 Oct;9(5):318–23. pmid:32789666
  25. 25. Ma IWY, Khan NA, Kang A, Zalunardo N, Palepu A. Systematic review identified suboptimal reporting and use of race/ethnicity in general medical journals. J Clin Epidemiol. 2007 Jun;60(6):572–8. pmid:17493512
  26. 26. Lu C, Ahmed R, Lamri A, Anand SS. Use of race, ethnicity, and ancestry data in health research. PLOS Global Public Health 2022;2(9):e0001060. pmid:36962630
  27. 27. Yu N, Chen FC, Ota S, Jorde LB, Pamilo P, Patthy L, et al. Larger genetic differences within africans than between Africans and Eurasians. Genetics. 2002 May;161(1):269–74. pmid:12019240
  28. 28. Sultan AH. Editorial: Obstetrical Perineal Injury and Anal Incontinence. Clin Risk. 1999 Nov 1;5(6):193–6.
  29. 29. Harvey MA, Pierce M, Alter JEW, Chou Q, Diamond P, Epp A, et al. Obstetrical Anal Sphincter Injuries (OASIS): Prevention, Recognition, and Repair. J Obstet Gynaecol Can JOGC J Obstet Gynecol Can JOGC. 2015 Dec;37(12):1131–48. pmid:26637088
  30. 30. American College of Obstetricians and Gynecologists’ Committee on Practice Bulletins—Obstetrics. Practice Bulletin No. 165: Prevention and Management of Obstetric Lacerations at Vaginal Delivery. Obstet Gynecol. 2016 Jul;128(1):e1–15. pmid:27333357
  31. 31. Koelbl H, Nitti V, Baessler K, Salvatore S, Sultan A, Yamaguchi O. Pathophysiology of Urinary Incontinence, Faecal Incontinence and Pelvic Organ Prolapse.
  32. 32. Gurol-Urganci I, Cromwell DA, Edozien LC, Mahmood TA, Adams EJ, Richmond DH, et al. Third- and fourth-degree perineal tears among primiparous women in England between 2000 and 2012: time trends and risk factors. BJOG Int J Obstet Gynaecol. 2013 Nov;120(12):1516–25. pmid:23834484
  33. 33. Ampt AJ, Patterson JA, Roberts CL, Ford JB. Obstetric anal sphincter injury rates among primiparous women with different modes of vaginal delivery. Int J Gynaecol Obstet Off Organ Int Fed Gynaecol Obstet. 2015 Dec;131(3):260–4. pmid:26489488
  34. 34. Chi Wai T, Cecilia CW, Anny TWM, Hau Yee L. Incidence and Risk Factors of Obstetric Anal Sphincter Injuries after Various Modes of Vaginal Deliveries in Chinese Women. Chin Med J (Engl). 2015 Sep 20;128(18):2420–5. pmid:26365956
  35. 35. McLeod NL, Gilmour DT, Joseph KS, Farrell SA, Luther ER. Trends in major risk factors for anal sphincter lacerations: a 10-year study. J Obstet Gynaecol Can JOGC J Obstet Gynecol Can JOGC. 2003 Jul;25(7):586–93. pmid:12851671
  36. 36. Marschalek M, Worda C, Kuessel L, Koelbl H, Oberaigner W, Leitner H, et al. Risk and protective factors for obstetric anal sphincter injuries: A retrospective nationwide study. Birth Berkeley Calif. 2018 Dec;45(4):409–15. pmid:29537100
  37. 37. Gurol-Urganci I, Bidwell P, Sevdalis N, Silverton L, Novis V, Freeman R, et al. Impact of a quality improvement project to reduce the rate of obstetric anal sphincter injury: a multicentre study with a stepped-wedge design. BJOG Int J Obstet Gynaecol. 2021 Feb;128(3):584–92. pmid:33426798
  38. 38. Shah NS, Kandula NR. Addressing Asian American Misrepresentation and Underrepresentation in Research. Ethn Dis. 2020;30(3):513–6. pmid:32742157
  39. 39. Byrd WM, Clayton LA. Race, medicine, and health care in the United States: a historical survey. J Natl Med Assoc. 2001 Mar;93(3 Suppl):11S–34S. pmid:12653395
  40. 40. Hoffman KM, Trawalter S, Axt JR, Oliver MN. Racial bias in pain assessment and treatment recommendations, and false beliefs about biological differences between blacks and whites. Proc Natl Acad Sci U S A. 2016 Apr 19;113(16):4296–301. pmid:27044069
  41. 41. Witherspoon DJ, Wooding S, Rogers AR, Marchani EE, Watkins WS, Batzer MA, et al. Genetic Similarities Within and Between Human Populations. Genetics. 2007 May;176(1):351–9. pmid:17339205
  42. 42. Hui W. The Idea of Asia and Its Ambiguities. J Asian Stud. 2010 Nov;69(4):985–9.
  43. 43. Kassen M. Understanding foreign policy strategies of Kazakhstan: a case study of the landlocked and transcontinental country. Camb Rev Int Aff. 2018 Jul 4;31(3–4):314–43.