I was arguing with a transphobe who asked for sources so I pulled this all together from around the web. Feel free to save/use it as necessary!
Here are statements of support for gender affirming care from:
Here’s some more sources and context:
Definitions & Framework
Measuring Sex, Gender Identity, and Sexual Orientation
The National Academies of Sciences, Engineering, and Medicine published this consensus report in 2022 to guide the National Institutes of Health on measuring sex, gender identity, and sexual orientation.
Methodology
- A multidisciplinary committee reviewed existing measures and research across clinical, administrative, and survey settings.
- Committee members developed consensus definitions and evaluated how different questions perform in different contexts.
Findings
- The report defines sex as a multidimensional construct based on a cluster of anatomical and physiological traits, including external genitalia, secondary sex characteristics, gonads, chromosomes, and hormones.
- The report defines gender as including identity, expression, and social position.
- The committee concluded that gender cannot be reduced to sex assigned at birth or to specific sex traits.
- The report recommends collecting the information required for the purpose at hand. It supports a two-step approach using sex assigned at birth and current gender when researchers need to identify transgender experience.
- The report recommends a separate intersex-status question when that information matters. It advises against treating intersex as a simple third response to a male-or-female sex question.
Limitations
- The report addresses measurement and conceptual clarity. It does not settle every philosophical dispute about the meaning of sex or gender.
- Recommended questions can require revision as terminology and evidence develop.
World Health Organization: Gender and Health
The World Health Organization distinguishes sex, gender, and gender identity in its public-health guidance.
What the source establishes
- Sex refers to biological and physiological characteristics such as chromosomes, hormones, and reproductive organs.
- Gender refers to socially constructed norms, roles, and relations.
- Gender identity refers to a person’s deeply felt internal experience of gender, which may or may not correspond to physiology or designated sex at birth.
- Sex, gender, and gender identity can each influence health and access to care.
Limitations
- This is institutional guidance rather than an original empirical study.
- Definitions vary somewhat across fields, so debates should identify whether the context is clinical, demographic, biological, or social.
American Psychological Association: Understanding Transgender People, Gender Identity and Gender Expression
The American Psychological Association provides definitions for transgender identity, gender identity, gender expression, and related terms.
What the source establishes
- Gender identity describes a person’s internal sense of gender.
- Gender expression describes how a person presents gender through appearance and behavior.
- Transgender describes people whose gender identity differs from the sex assigned to them at birth.
- Gender identity, gender expression, and sexual orientation describe separate concepts.
Limitations
- The page summarizes professional guidance and research. Use its linked scholarship for contested causal claims.
Sex Development, Chromosomes & Intersex Variation
Sex Redefined
Claire Ainsworth’s 2015 Nature feature reviews research on differences of sex development, chimerism, and cellular sex.
Methodology
- This is a science-journalism feature based on interviews and published research.
- It follows sex development across chromosomes, genes, gonads, hormones, anatomy, and cells.
Findings
- Typical XX and XY development accounts for most people, while variations can produce discordance among chromosomal, gonadal, hormonal, and anatomical traits.
- Genetic changes, mosaicism, chimerism, hormone production, and hormone-response differences can affect the developmental pathway.
- A single chromosome test cannot describe every sex-related trait in every person.
Limitations
- The article provides a synthesis for general readers. It is not a primary prevalence study.
- The article uses “spectrum” as a broad description of trait variation. Reproductive biology still recognizes two gamete types.
How Sexually Dimorphic Are We? Review and Synthesis
Blackless, Charuvastra, Derryck, Fausto-Sterling, Lauzanne, and Lee published this review in the American Journal of Human Biology in 2000.
Methodology
- The authors reviewed medical literature on chromosomal, gonadal, hormonal, and anatomical variation.
- They combined prevalence estimates for conditions that departed from an ideal of complete sexual dimorphism.
Findings
- The authors estimated that about 1.7% of live births show some departure from complete chromosomal, gonadal, genital, or hormonal dimorphism under their broad definition.
- The estimate became the main source for the widely repeated 1.7% figure.
Limitations
- Late-onset congenital adrenal hyperplasia contributes most of the estimate. Many people counted by the paper have unambiguous genitalia and identify as male or female.
- The paper’s category is broader than definitions centered on ambiguous genitalia or discordance between chromosomal and phenotypic sex.
- The number should always appear with the definition used to produce it.
SRY Gene: MedlinePlus Genetics
The National Library of Medicine explains the role of SRY in sex development and describes conditions that can result when the pathway changes.
What the source establishes
- SRY usually appears on the Y chromosome and helps direct development of the testes.
- SRY variants account for a portion of 46,XY complete gonadal dysgenesis, also called Swyer syndrome.
- An SRY translocation onto an X chromosome can contribute to 46,XX testicular differences of sex development.
Limitations
- SRY provides one part of a larger pathway that includes many genes, hormones, receptors, and tissues.
- The page provides clinical orientation rather than prevalence estimates for every condition.
Swyer Syndrome: MedlinePlus Genetics
Swyer syndrome, or 46,XY complete gonadal dysgenesis, provides a documented example of chromosomal and phenotypic traits developing along different paths.
What the source establishes
- People with Swyer syndrome have a 46,XY karyotype and female-typical external genitalia.
- They usually have a uterus and fallopian tubes because typical testicular hormone production did not occur during development.
- Their gonads do not function as ovaries, so pregnancy requires donated oocytes and medical support.
Limitations
- Swyer syndrome is rare.
- The condition demonstrates variation in sex development. It does not show that chromosomes lack biological importance.
Pregnancy and Delivery in a Patient With Pure 46,XY Karyotype
Poláková and colleagues published this case report and literature review in 2013.
Methodology
- The authors described a patient with 46,XY complete gonadal dysgenesis who became pregnant through in vitro fertilization using a donated oocyte.
- They reviewed previous reports of pregnancy in patients with 46,XY gonadal dysgenesis.
Findings
- The patient carried a pregnancy and delivered a healthy child.
- The case documents that a Y chromosome does not prevent gestation when a uterus is present and assisted reproduction supplies an oocyte and hormonal support.
Limitations
- This is a rare case report rather than a prevalence study.
- The patient did not produce an oocyte, and the case does not establish typical fertility for people with Swyer syndrome.
Gender Development & Neuroscience
Patterns of Gender Development
Martin and Ruble published this developmental-psychology review in the Annual Review of Psychology in 2010.
Methodology
- The authors reviewed research on children’s gender concepts, identity, stereotypes, preferences, and behavior.
- The review considered cognitive development, motivation, social learning, family, peers, and culture.
Findings
- Children actively organize information about gender and apply it to themselves and other people.
- Gender development reflects interactions among cognition, motivation, social environment, and biological development.
- Children develop gender labels before they develop a complete understanding of gender stability and constancy.
Limitations
- Much of the literature comes from Western populations.
- The review addresses gender development broadly and provides limited direct evidence about transgender identity.
Sex Beyond the Genitalia: The Human Brain Mosaic
Joel and colleagues published this analysis in Proceedings of the National Academy of Sciences in 2015.
Methodology
- The authors analyzed magnetic-resonance imaging datasets containing more than 1,400 brains.
- They identified features showing the largest average sex differences and tested whether individual brains consistently contained male-typical or female-typical features.
- They applied a related analysis to behavioral datasets containing more than 5,500 people.
Findings
- Most brains contained a mixture of features that appeared more often in males, more often in females, or commonly in both groups.
- Fully internally consistent male-typical or female-typical profiles were uncommon under the authors’ method.
- Average group differences can coexist with extensive overlap and within-person variation.
Limitations
- Critics showed that multivariate models can classify sex from structural brain patterns at rates above chance. The disagreement concerns whether accurate classification establishes two internally consistent brain types.
- The study examined sex-related brain features. It did not test transgender identity directly.
Structural, Functional, and Metabolic Brain Differences as a Function of Gender Identity or Sexual Orientation
Frigerio, Ballerini, and Valdés Hernández published this systematic review in Archives of Sexual Behavior in 2021.
Methodology
- The authors systematically reviewed human neuroimaging literature through 2018 and discussed later studies published through March 2021.
- The review included 39 studies concerning gender identity and 24 concerning sexual orientation.
Findings
- Some structural and functional features among transgender participants resembled patterns associated with their gender identity.
- Many features remained closer to patterns associated with sex assigned at birth, and other findings appeared intermediate or distinct.
- The literature did not reveal a single reliable neuroanatomical marker of transgender identity.
Limitations
- Many studies used small samples and different imaging methods.
- Hormone exposure, age, sexual orientation, scanner differences, and analytic choices complicated comparisons.
- Cross-sectional findings cannot establish whether a difference preceded gender incongruence or developed through later experience.
The Neuroanatomy of Transgender Identity: Mega-Analytic Findings From the ENIGMA Transgender Persons Working Group
Mueller and colleagues published this multi-site structural MRI analysis in the Journal of Sexual Medicine in 2021.
Methodology
- The researchers pooled data from eight sites and analyzed 803 participants.
- The sample included 214 transgender men, 172 transgender women, 221 cisgender men, and 196 cisgender women who had not received gender-affirming hormones.
- The study compared cortical thickness, surface area, and subcortical volume while correcting for multiple comparisons.
Findings
- The analysis found no significant group differences in cortical thickness after correction.
- Differences in surface area and subcortical volume did not amount to a simple shift from one cisgender group toward the other.
- The authors described the results as a distinct neuroanatomical pattern rather than a complete masculinization or feminization of the brain.
Limitations
- The study was cross-sectional and cannot establish cause or developmental timing.
- Pooling data across scanners and sites adds heterogeneity.
- Group averages cannot identify an individual’s gender.
A Sex Difference in the Human Brain and Its Relation to Transsexuality
Zhou and colleagues published this postmortem study in Nature in 1995.
Methodology
- The authors measured the central subdivision of the bed nucleus of the stria terminalis in postmortem brain tissue.
- They compared a small number of transgender women with male and female reference groups.
Findings
- The measured region in the transgender women fell within the female-typical range reported by the study.
- The authors reported that the finding did not track sexual orientation in their comparison cases.
Limitations
- The transgender sample was extremely small.
- Most transgender participants had received long-term hormone therapy.
- Adult postmortem data cannot establish whether the difference caused, followed, or merely correlated with gender identity.
Sex Reassignment at Birth: Long-Term Review and Clinical Implications
Diamond and Sigmundson published this follow-up of David Reimer in Archives of Pediatrics and Adolescent Medicine in 1997.
Methodology
- The authors followed an XY child whose penis had been destroyed during infancy and who was then surgically reassigned and raised as a girl.
- They interviewed the patient, his family, and clinicians about development and later identity.
Findings
- Reimer rejected the female sex of rearing and began living as male during adolescence.
- The outcome contradicted earlier reports that described the reassignment as successful.
- The case undermined the claim that rearing alone can reliably determine gender identity.
Limitations
- One unusual clinical case cannot determine the relative contribution of biology and environment across the population.
- Reimer experienced major medical trauma, secrecy, repeated examinations, and family distress. Those factors limit broad causal claims.
Social & Historical Dimensions of Gender
Standards of Care for the Health of Transgender and Gender Diverse People, Version 8
The World Professional Association for Transgender Health published Version 8 of its standards in 2022. This section uses the document for terminology and cross-cultural context rather than treatment outcomes.
What the source establishes
- Gender-diverse identities and social categories appear across cultures and languages.
- Terms such as hijra, fa’afafine, travesti, muxe, and Two-Spirit have distinct cultural histories and do not translate cleanly into one English category.
- Transgender and nonbinary function as broad contemporary terms, while culturally specific terms should retain their local meaning.
Limitations
- WPATH provides clinical guidance and professional consensus. It does not supply a single anthropological history of every cultural group.
- Examples from one culture should not be treated as interchangeable with identities from another culture.
United Nations Free & Equal: Celebrate Trans Visibility
The United Nations Human Rights Office identifies several culturally specific gender-diverse traditions, including hijra, Two-Spirit, travesti, fa’afafine, and transpinay.
What the source establishes
- Gender diversity has deep historical and cultural roots in many societies.
- Contemporary English vocabulary does not exhaust the ways societies organize gender.
Limitations
- This is a human-rights educational source.
- It provides examples rather than a systematic anthropological review.
Clinical Classification & Professional Positions
American Psychiatric Association: Gender Dysphoria Diagnosis
The American Psychiatric Association explains how the DSM-5 and DSM-5-TR distinguish transgender identity from gender dysphoria.
What the source establishes
- Gender nonconformity does not constitute a mental disorder by itself.
- Gender dysphoria refers to clinically significant distress or impairment associated with gender incongruence.
- A transgender person may experience gender dysphoria, although transgender identity does not automatically produce the diagnosis.
Limitations
- Diagnostic manuals classify conditions for clinical use. They do not provide a complete theory of gender identity.
- The diagnosis remains debated because it can help people access care while also carrying a history of pathologization.
World Health Organization: Gender Incongruence and Transgender Health in the ICD
The World Health Organization explains the treatment of gender incongruence in ICD-11.
What the source establishes
- ICD-11 replaced older categories such as “transsexualism” and “gender identity disorder of children.”
- WHO moved gender incongruence out of the chapter on mental and behavioral disorders.
- ICD-11 places gender incongruence in the chapter on conditions related to sexual health so health systems can continue to code relevant care.
Limitations
- Classification reflects clinical utility and expert review. It does not turn every policy position about trans people into a medical conclusion.
American Psychological Association Resolution on Gender Identity Change Efforts
The American Psychological Association adopted this resolution opposing efforts that aim to change a person’s gender identity or gender expression.
What the source establishes
- APA opposes portrayals of transgender and nonbinary people as mentally ill because of their identities or expressions.
- APA states that gender-identity change efforts lack adequate scientific support and carry a risk of harm.
Limitations
- This is an organizational policy resolution rather than an original experiment.
- A professional resolution establishes the association’s position. It does not eliminate the need to inspect the cited evidence for a specific empirical claim.
Trans People in Sports
Sport and Transgender People: A Systematic Review of the Literature Relating to Sport Participation and Competitive Sport Policies
Jones, Arcelus, Bouman, and Haycraft published this systematic review in Sports Medicine in 2017.
Methodology
- The authors reviewed eight empirical studies and 31 competitive-sport policies.
- The evidence included studies of hormone-related physiology and a small amount of direct performance data.
Findings
- The review found no direct and consistent evidence of an overall competitive advantage across the sparse literature available at the time.
- The authors found that many policies lacked a clear evidentiary basis and varied substantially across organizations.
Limitations
- Only eight empirical studies met the criteria, and very few studied trained or elite athletes.
- The conclusion reflects insufficient direct evidence in 2017. It cannot establish that no performance differences exist.
- Later studies provide additional information about strength, lean mass, hemoglobin, and running performance.
Effect of Gender-Affirming Hormones on Athletic Performance in Transwomen and Transmen
Roberts, Smalley, and Ahrendt published this retrospective study of U.S. Air Force personnel in the British Journal of Sports Medicine in 2021.
Methodology
- The researchers analyzed annual fitness-test records before and after the start of gender-affirming hormone therapy.
- Tests included push-ups, sit-ups, and a 1.5-mile run.
- The cohort included military personnel rather than elite athletes.
Findings
- Before hormone therapy, trans women completed 31% more push-ups and 15% more sit-ups and ran 21% faster than cisgender women in the comparison group.
- After two years of feminizing hormone therapy, push-up and sit-up differences were no longer statistically significant.
- Trans women still ran about 12% faster on average after two years in this cohort.
- Trans men reached or exceeded the cisgender male average for several tests after testosterone therapy.
Limitations
- The study used military fitness data, which do not measure elite sport performance.
- Training history, adherence, and other confounders remained outside the researchers’ control.
- Average group differences do not determine the outcome of a particular athlete or event.
How Does Hormone Transition in Transgender Women Change Body Composition, Muscle Strength and Haemoglobin?
Harper and colleagues published this systematic review in the British Journal of Sports Medicine in 2021.
Methodology
- The authors reviewed studies of transgender women receiving feminizing hormone therapy.
- They focused on lean body mass, muscle area, strength, and hemoglobin because these traits can affect athletic performance.
Findings
- Hemoglobin generally moved into the cisgender female range after several months of hormone therapy.
- Lean body mass, muscle area, and strength declined during treatment.
- Some differences in strength and lean mass could remain after 12 to 36 months.
Limitations
- Most participants were not athletes.
- The studies measured physiological proxies more often than performance in a specific sport.
- Study size, treatment duration, and methods varied substantially.
Strength, Power and Aerobic Capacity of Transgender Athletes: A Cross-Sectional Study
Hamilton and colleagues published this laboratory study in the British Journal of Sports Medicine in 2024.
Methodology
- The researchers tested 19 cisgender men, 12 transgender men, 23 transgender women, and 21 cisgender women who participated in competitive sports or structured training.
- Tests included body composition, grip strength, jump performance, lung function, and maximal oxygen uptake.
Findings
- Trans women had higher absolute grip strength than cisgender women in this sample.
- Trans women had lower jump height relative to fat-free mass and lower maximal oxygen uptake relative to body weight than cisgender women.
- Absolute maximal oxygen uptake did not differ significantly between trans women and cisgender women.
- Results varied by metric, which supports direct study of sport-relevant performance rather than a single proxy.
Limitations
- The study was cross-sectional and cannot show how an individual changed during hormone therapy.
- The groups were small and differed in age, height, weight, sport, and training history.
- Laboratory measures do not directly predict medals, rankings, or injury risk in every sport.
Bathrooms, Safety & Public Accommodations
Gender Identity Nondiscrimination Laws in Public Accommodations: Evidence Regarding Safety and Privacy
Hasenbush, Flores, and Herman published this study in Sexuality Research and Social Policy in 2019.
Methodology
- The authors matched Massachusetts localities with gender-identity-inclusive public-accommodation ordinances to localities without comparable ordinances.
- They obtained police incident reports involving assault, sex crimes, and voyeurism in restrooms, locker rooms, and changing rooms.
- They compared incident patterns before and after the policies took effect.
Findings
- Inclusive ordinances were not associated with an increase in the number or frequency of reported safety and privacy incidents.
- Reported incidents in these facilities were rare in both sets of localities.
Limitations
- The study covers Massachusetts and may not capture every local context.
- Police reports omit incidents that victims never report.
- The rarity of recorded incidents limits the ability to detect very small changes.
2022 U.S. Trans Survey: Public Life
The 2022 U.S. Trans Survey provides updated self-reported information about transgender people’s experiences in public restrooms.
Methodology
- The survey collected online responses from 92,329 transgender people age 16 or older in the United States and its territories.
- The project used community outreach and received institutional review board approval from UCLA.
Findings
- Four percent of respondents reported being denied restroom access during the previous year.
- Six percent reported verbal harassment, physical attack, or unwanted sexual contact while accessing or using a restroom during the previous year.
Limitations
- The survey used a large nonprobability sample, so it cannot provide a nationally representative prevalence estimate.
- Self-selection and recall can affect the results.
- The survey documents respondents’ experiences. It does not test the effect of a specific law.
Language, Pronouns & Singular They
Oxford English Dictionary: A Brief History of Singular They
The Oxford English Dictionary traces singular “they” to the medieval romance William and the Werewolf, written around 1375.
What the source establishes
- English speakers have used “they” with a singular antecedent for more than six centuries.
- The older use commonly referred to an unknown, indefinite, or generic person.
- The pronoun’s contemporary use for a known nonbinary person extends an established singular pattern.
Limitations
- Historical use of indefinite singular “they” does not mean every earlier writer used it as a nonbinary identity pronoun.
- Grammar history establishes linguistic legitimacy. It does not settle broader political disagreements about gender.
APA Style: Singular They
The American Psychological Association’s style guide directs writers to use a person’s self-identified pronouns, including singular they.
What the source establishes
- APA Style accepts singular “they” for an unknown or generic person.
- APA Style accepts singular “they” for a known person who uses that pronoun.
- Standard agreement remains plural in form, as in “they are.”
Limitations
- A style guide sets a writing standard. It does not serve as an empirical study of mental-health outcomes or social policy.
Social Transition & Trans Youth
Gender Identity 5 Years After Social Transition
Olson and colleagues published this longitudinal study in Pediatrics in 2022.
Methodology
- The researchers followed 317 children who had socially transitioned between ages 3 and 12.
- The children entered the study at an average age of 8 and received repeated follow-up over about five years.
- The study recorded whether participants identified as transgender, nonbinary, or cisgender at follow-up.
Findings
- At the end of the study period, 94% identified as binary transgender.
- About 3.5% identified as nonbinary.
- About 2.5% identified as cisgender.
- Later retransition occurred more often among children who had socially transitioned before age 6 than among those who transitioned at age 6 or older.
Limitations
- The sample included children with supportive families who had already completed a social transition.
- Most participants were White and came from families with relatively high incomes.
- The study describes identity trajectories in this cohort. It cannot determine the outcome for every gender-questioning child.
- Five years does not provide lifetime follow-up.
Mental Health and Self-Worth in Socially Transitioned Transgender Youth
Durwood, McLaughlin, and Olson published this study in the Journal of the American Academy of Child and Adolescent Psychiatry in 2017.
Methodology
- The researchers compared socially transitioned transgender children with age-matched and gender-matched cisgender controls and with siblings.
- Children and parents completed standardized measures of depression, anxiety, and self-worth.
Findings
- Transgender participants showed depression and self-worth scores comparable to the control groups.
- Anxiety was slightly higher among transgender participants, although it remained below levels reported in many earlier clinical samples.
Limitations
- The study was cross-sectional and lacked mental-health measurements from before social transition.
- Families volunteered for a research project and generally supported their children.
- The results establish an association in this sample and cannot prove that social transition caused the observed mental-health profile.
Discrimination, Victimization & Minority Stress
A Systematic Review of Social Stress and Mental Health Among Transgender and Gender-Nonconforming People in the United States
Valentine and Shipherd published this systematic review in Clinical Psychology Review in 2018.
Methodology
- The authors reviewed U.S. research on stigma, discrimination, victimization, rejection, concealment, and mental health among transgender and gender-nonconforming people.
- They organized the evidence using minority-stress theory.
Findings
- Studies consistently associated discrimination, rejection, and victimization with depression, anxiety, substance use, suicidal thoughts, and suicide attempts.
- Social support, identity pride, and community connection appeared as protective factors in portions of the literature.
- The review located mental-health disparities within chronic social stressors rather than treating transgender identity as an inherent pathology.
Limitations
- Most included studies were cross-sectional and used convenience samples.
- Measures and terminology varied across studies.
- Associations between stress and mental health can run in more than one direction, although longitudinal and daily-diary research strengthens the minority-stress explanation.
Gender Identity Disparities in Criminal Victimization: National Crime Victimization Survey, 2017–2018
Flores, Meyer, Langton, and Herman analyzed nationally representative National Crime Victimization Survey data and published their study in the American Journal of Public Health in 2021.
Methodology
- The researchers pooled 2017 and 2018 NCVS data for people age 16 and older.
- They compared violent and property victimization rates for transgender and cisgender respondents.
Findings
- Transgender respondents experienced 86.2 violent victimizations per 1,000 people, compared with 21.7 per 1,000 cisgender people.
- The estimated rate was about four times higher for transgender people.
- About half of violent victimizations were not reported to police in both populations.
Limitations
- The number of transgender respondents was much smaller than the number of cisgender respondents, which widens uncertainty for subgroup estimates.
- The data combine two years and do not establish the cause of each disparity.
- Survey wording and disclosure can affect identification of transgender respondents.
2022 U.S. Trans Survey: Safety
The 2022 U.S. Trans Survey documents recent experiences of harassment, unequal treatment, violence, and interactions with law enforcement.
Findings
- Thirty percent of respondents reported verbal harassment during the previous year because of gender identity or expression.
- Three percent reported a physical attack during the previous year for the same reason.
- Nine percent reported denial of equal treatment or service.
- Seventy-three percent reported some level of discomfort asking police for help, including 47% who felt very uncomfortable.
Limitations
- The sample is large and diverse but not nationally representative.
- The survey relies on self-report and cannot independently verify every incident.
- Advocacy organizations conducted the survey with an academic advisory structure and UCLA institutional review board approval. Readers should consider both the methodology and the sponsoring organizations.
2022 U.S. Trans Survey: Health and Wellbeing
The health report examines support, discrimination, transition, and self-reported health among respondents.
Findings
- Respondents with supportive families reported lower lifetime suicidal thoughts than respondents with unsupportive families, 78% compared with 88%.
- Past-year suicidal thoughts rose from 31% among respondents reporting no discrimination or harassment to 50% among those verbally harassed and 63% among those physically assaulted.
- Respondents who had socially or medically transitioned reported higher happiness, thriving, and life satisfaction than respondents who had not.
Limitations
- Cross-sectional comparisons cannot establish causation.
- The survey did not use a probability sample.
- Differences between groups can reflect age, access to care, income, family support, and other factors that require statistical analysis beyond raw percentages.