Perceived psychosocial impacts of legalized same-sex marriage: A scoping review of sexual minority adults’ experiences

A growing body of literature provides important insights into the meaning and impact of the right to marry a same-sex partner among sexual minority people. We conducted a scoping review to 1) identify and describe the psychosocial impacts of equal marriage rights among sexual minority adults, and 2) explore sexual minority women (SMW) perceptions of equal marriage rights and whether psychosocial impacts differ by sex. Using Arksey and O’Malley’s framework we reviewed peer-reviewed English-language publications from 2000 through 2019. We searched six databases (PubMed, PsycINFO, CINAHL, Web of Science, JSTOR, and Sociological Abstracts) to identify English language, peer-reviewed journal articles reporting findings from empirical studies with an explicit focus on the experiences and perceived impact of equal marriage rights among sexual minority adults. We found 59 studies that met our inclusion criteria. Studies identified positive psychosocial impacts of same-sex marriage (e.g., increased social acceptance, reduced stigma) across individual, interpersonal (dyad, family), community (sexual minority), and broader societal levels. Studies also found that, despite equal marriage rights, sexual minority stigma persists across these levels. Only a few studies examined differences by sex, and findings were mixed. Research to date has several limitations; for example, it disproportionately represents samples from the U.S. and White populations, and rarely examines differences by sexual or gender identity or other demographic characteristics. There is a need for additional research on the impact of equal marriage rights and same-sex marriage on the health and well-being of diverse sexual minorities across the globe.


Introduction
Legalization of same-sex marriage represents one important step toward advancing equal rights for sexual and gender minorities. Over the past two decades same-sex marriage has become legally recognized in multiple countries around the world. Between 2003 and mid-2015, same-sex couples in the United States (U.S.) gained the right to marry in 37 of 50 states. This right was extended to all 50 states in June 2015, when the U.S. Supreme Court ruled in Obergefell v. Hodges that same-sex couples in all U.S. states had equal marriage rights. As of October 2019, same-sex couples had the right to marry in 30 countries and territories around the world [1].
National laws or policies that extend equal marriage rights to same-sex couples signal a reduction in structural stigma and have the potential to positively impact the health and wellbeing of sexual minorities. Structural stigma refers to norms and policies on societal, institutional and cultural levels that negatively impact the opportunities, access, and well-being of a particular group [2]. Forms of structural stigma that affect sexual minorities-such as restrictions on same-sex marriage-reflect and reinforce the social stigma against non-heterosexual people that occurs at individual, interpersonal, and community levels [3]. According to Hatzenbuehler and colleagues, structural stigma is an under-recognized contributor to health disparities among stigmatized populations [4][5][6], and reductions in structural stigma can improve health outcomes among sexual minorities [7,8].
Marriage is a fundamental institution across societies and access to the right to marry can reduce sexual-minority stigma by integrating sexual minority people more fully into society [9]. Same-sex marriage also provides access to a wide range of tangible benefits and social opportunities associated with marriage [9,10]. Despite the benefits of marriage rights, sexual minorities continue to experience stigma-related stressors, such as rejection from family or community, and discrimination in employment and other life spheres [11]. In addition, reactions to samesex marriage appear to differ among sexual minorities and range from positive to ambivalent [11][12][13]. Extending marriage rights to same-sex couples remedies only one form of structural stigma. Although legalization of same-sex marriage represents a positive shift in the social and political landscape, the negative impact of social stigma may persist over time. For example, a recent Dutch study found that despite 20 years of equal marriage rights, sexual minority adolescents continue to show higher rates of substance use and lower levels of well-being than their heterosexual peers [14]. This study underscores the importance of understanding the complex impact of stigma at the structural, community, interpersonal, and individual levels.

Impact on sexual minority health
A growing body of literature, using different methods from diverse countries where same-sex marriage has been debated or adopted, provides important insights into the impact of equal marriage rights on the health and well-being of sexual minority individuals. Research to date has consistently found that legal recognition of same-sex marriage has a positive impact on health outcomes among sexual and gender minority populations [15][16][17][18][19][20]. Studies in the U.S. have found evidence of reduced psychological distress and improved self-reported health among sexual minorities living in states with equal marriage rights compared to those living in states without such rights [5,[21][22][23]. One state-specific study also found improved health outcomes for sexual minority men after legalization of same-sex marriage [24]. Furthermore, sexual minorities living in states that adopted, or were voting on, legislation restricting marriage recognition to different-sex couples reported higher rates of alcohol use disorders and psychological distress compared to those living in states without such restrictions [5,[25][26][27][28][29][30][31]. Consistent with research in the U.S., findings from research in Australia on marriage restriction voting, found that sexual minorities living in jurisdictions where a majority of residents voted in support of same-sex marriage reported better overall health, mental health, and life satisfaction than sexual minorities in locales that did not support same-sex marriage rights [32].
Although existing literature reviews have documented positive impacts of equal marriage rights on physical and mental health outcomes among sexual minority individuals [15][16][17][18][19][20], to our knowledge no reviews have conducted a nuanced exploration of the individual, interpersonal, and community impacts of legalized same-sex marriage. An emerging body of quantitative and qualitative literature affords a timely opportunity to examine a wide range of psychosocial impacts of equal marriage rights. Understanding these impacts is important to guide and interpret future research about the potential protective health effects of same-sex marriage.

Potential differences between SMW and SMM
Given the dearth of research focusing on the health and well-being of sexual minority women (SMW), especially compared to the sizable body of research on sexual minority men (SMM) [33,34], there is a need to explore whether the emerging literature on same-sex marriage provides insights about potential differences in psychosocial impacts between SMW and SMM. Recent research underscores the importance of considering SMW's perspectives and experiences related to same-sex marriage. For example, gendered social norms play out differently for women and men in same-sex and different-sex marriages, and interpersonal dynamics and behaviors, including those related to coping with stress, are influenced by gender socialization [35]. However, there is little research about how societal-level gender norms and gendered social constructions of marriage may be reflected in SMW's perceptions of same-sex marriage. Structural sexism (e.g., gendered power and resource inequality at societal and institutional levels) differentially impacts women's and men's health [36], and may also contribute to sex differences in experiences and impacts of same-sex marriage. For example, research from the U.S. suggests that same-sex marriage rights may improve health outcomes and access to healthcare for SMM, but evidence is less robust for SMW [37][38][39]. Differences in health outcomes appear to be at least partially explained by lower socioeconomic status (income, employment status, perceived financial strain) among SMW compared to SMM [40]. Further, other psychosocial factors may contribute to differential experiences of legalized same-sex marriage. For example, a study of older sexual minority adults in states with equal marriage rights found that married SMW experienced more LGBTQ (lesbian, gay, bisexual, transgender, queer) microaggressions than single SMW, but no differences by relationship status were noted among SMM [41]. Mean number of microaggressions experienced by SMW in partnered unmarried relationships fell between, but were not significantly different from, that of married and single SMW.

Theoretical framework
Social-ecological and stigma theoretical perspectives were used as the framework for organizing literature in this review (See Fig 1). Stigma occurs and is experienced by sexual minorities at individual, interpersonal, and structural levels, which mirror the levels of focus within the social-ecological framework [6,42]. Consequently, changes such as extending equal marriage rights to same-sex couples may influence sexual minorities' experiences of stigma across all of these levels [43]. Gaining access to the institution of marriage is distinct from marital status (or being married) and likely impacts sexual minority adults across individual, interpersonal, and community contexts [44], regardless of relationship status.
From a social-ecological perspective, individual and interpersonal processes can amplify or weaken the impact of structural level policies, such as equal marriage rights, on sexual minority individuals' health and well-being [43,45,46]. For example, on an individual level, experiences and perceptions of equal marriage rights may influence stigma-related processes such as internalized heterosexism, comfort with disclosure, and centrality of sexual identity [47]. Interpersonal and community level interactions may trigger stigma-related processes such as prejudice concerns, vigilance, or mistrust. Such processes may in turn, influence the impact of social policy change on sexual minority stress and well-being [48][49][50].
The impact of equal marriage rights among sexual minority individuals may also be influenced by other social and political factors such as state-or regional-level social climate [50-52], or inconsistency among other policy protections against discrimination (e.g., in housing or public accommodations) [11,50]. Sociopolitical uncertainty may continue long after the right to marry is extended to same-sex couples [53,54]. Monk and Ogolsky [44] define political uncertainty as a state of "having doubts about legal recognition bestowed on individuals and families by outside systems; being unsure about social acceptance of marginalized relationships; being unsure about how 'traditional' social norms and roles pertain to marginalized relationships or how alternative scripts might unfold" (p. 2).

Current study
The overall aim of this scoping review was to identify and summarize existing literature on psychosocial impacts of equal marriage rights among sexual minority adults. Specific objectives were to: 1) identify and describe the psychosocial impacts of equal marriage rights on sexual minority adults; and 2) explore SMW-specific perceptions of equal marriage rights and whether psychosocial impacts differ for SMM and SMW.

Study design
We used a scoping review approach, as it is well-suited for aims designed to provide a descriptive overview of a large and diverse body of literature [55]. Scoping reviews have become a widely used approach for synthesizing research evidence, particularly in health-related fields [55]. Scoping reviews summarize the range of research, identify key characteristics or factors related to concepts, and identify knowledge gaps in particular areas of study [56,57]. By contrast, systematic reviews are more narrowly focused on creating a critically appraised synthesized answer to a particular question pertinent to clinical practice or policy making [57]. We aimed to characterize and summarize research related to psychosocial impacts of equal marriage rights and same-sex marriage, including potential gaps in research specific to SMW. Following Arksey and O'Malley [56], the review was conducted using the following steps: 1) identifying the research question, 2) identifying relevant studies, 3) selecting studies, 4) charting the data, and 5) collating, summarizing and reporting results. Because this is a scoping review, it was not registered with PROSPERO, an international registry for systematic reviews.

Selection method
The authors used standard procedures for conducting scoping reviews, including following PRISMA guidelines [58]. Articles that report findings from empirical studies with an explicit focus on the psychosocial impacts of equal marriage rights and same-sex marriage on sexual minority adults are included in this review. All database searches were limited to studies in English language journals published from 2000 through 2019 (our most recent search was executed in June 2020). This time frame reflects the two decades since laws regarding same-sex marriage began to change in various countries or jurisdictions within countries. Literature review articles and commentaries were excluded. To ensure that sources had been vetted for scientific quality by experts, only articles in peer-reviewed journals were included; books and research in the grey literature (e.g., theses, dissertations, and reports) were excluded. There was no restriction on study location. A librarian searched PubMed, PsycINFO, CINAHL (Cumulative Index to Nursing and Allied Health Literature), Web of Science, JSTOR, and Sociological Abstracts databases using combinations of key search terms. Following is an example of the search terms used in CINAHL database searches: ((TI "marriage recognition" OR AB "marriage recognition") OR (TI marriage OR AB marriage) OR (TI same-sex OR AB same-sex) OR (TI "same sex" OR AB "same sex")) AND ((TI LGBT OR AB LGBT) OR (TI gay OR AB gay) OR (TI lesbian OR AB lesbian) OR (TI bisexual OR AB bisexual) OR (TI transgender OR AB transgender) OR (TI Obergefell OR AB Obergefell) OR (TI "sexual minorities" OR AB "sexual minorities)) Articles were selected in two stages of review. In stage one, the first author and librarian independently screened titles and abstracts for inclusion or exclusion using eligibility criteria. We excluded articles focused solely on the impact of relationship status on health outcomes, satisfaction or dynamics within marriage relationships, or the process of getting married (e.g., choices of who to invite, type of ceremony), or other topics that did not pertain directly to the research aims. For example, a study about the impact of getting married that also included themes pertaining to the impact or meaning of equal marriage rights was included in the full review. The first author and a librarian met to review and resolve differences and, in cases where relevance was ambiguous, articles underwent a full-text review (in stage 2). Table 1 summarizes exclusion categories used in the title and abstract reviews.
In stage two, articles not excluded in stage one were retrieved for full-text review. Each article was independently reviewed by two authors to assess study relevance. Discrepancies related to inclusion were few (less than 10%) and resolved through discussion and consensus-building among the first four authors. This process resulted in an analytic sample of 59 articles (see Fig 2). Table 2 provides an overview of characteristics of the studies included in this scoping review. Most were qualitative and most aggregated SMW and SMM in analyses. Only 14 studies explored differences in impact for SMW and SMM, or separately examined the specific perceptions and experiences of SMW. Although search terms were inclusive of transgender individuals, samples in the studies we reviewed rarely included or focused explicitly on experiences of transgender or gender nonbinary identified individuals. In studies that explicitly included transgender and nonbinary individuals, sample sizes were rarely large enough to permit examination of differences based on gender identity (e.g., survey samples with 2-3% representation of nonbinary or transgender individuals) [44, [59][60][61][62][63]. Other studies recruiting sexual

Exclusion Category Description (if applicable)
Not written in English ------Not peer-reviewed Conference proceedings, books and book chapters, magazine or news articles, theses/dissertations, reports and unpublished grey literature Not an empirical study Commentaries and editorials.

Review articles
Articles that did not present original research (e.g., systematic reviews, metaanalyses).
Not focused on adults Articles focused on children or adolescents only Not relevant Articles that did not focus on psychosocial impacts of marriage legalization (e.g., legal analyses of marriage policies, dynamics in married relationships).

No sexual or gender minority (SGM) focus
Articles that did not sample SGM individuals or that did not focus on impacts in relation to sexual and gender minorities https://doi.org/10.1371/journal.pone.0249125.t001 minorities may have included transgender and nonbinary individuals (who also identified as sexual minorities), but did not assess gender identity. Among studies in which participant race/ethnicity was reported, most included samples that were majority White. Studies of the impact of legalized marriage on physical health were not excluded in the original search parameters; however, physical health has been addressed in prior reviews [15][16][17][18][19][20]. Further, because our research questions focused on psychosocial factors, we excluded studies on physical health unless they also addressed individual, interpersonal, or community psychosocial impacts of same-sex marriage legalization. Studies that focused on physical health impacts or access to health insurance were used only in the introduction.
Civil union was not explicitly included as a search parameter, but articles focusing on civil unions were captured in our search. Although civil unions are not equivalent to marriage, they often confer similar substantive legal rights. We included articles about civil union that explicitly pertained to our research question, such as a study that examined perceived stigma and discrimination before and after implementation of civil union legislation in one U.S. state [64], and excluded articles that did not (e.g., a study of relationship quality or longevity among same-sex couples in civil unions) [65]. Multiple countries 4 (7) Sample Composition-Sex/Gender Only women 8 (14) Only men 3 (5) Mixed sex and gender 32 (54) Mixed sex and gender (transgender and nonbinary measured separately).

(14)
Not reported 8 (14) Sample A majority of the studies were conducted in the U.S. Of the 43 U.S. studies, 20 sampled from a single state, 10 included participants from multiple states, 12 used a national sample, and one had no human subjects (secondary analysis of legal cases). Of those sampling a single state, all focused on the impact of changes (or proposed changes) in same-sex marriage policy: 10 focused on Massachusetts (the first state in the U.S. to legalize same-sex marriage), two focused on Iowa, two on Vermont, and two on California. One article each included study participants from Nebraska, Oregon, Illinois, and a small (unnamed) non-metropolitan town in the Midwest.

Analysis method
We created a data extraction form to ensure consistency across team members in extracting key study information and characteristics including study design (e.g., quantitative, qualitative, or mixed method), location (e.g., country and/or region), sample (e.g., whether the study included or excluded SMW or SMM, assessed and reported race/ethnicity), and key results. Articles were also classified based on findings related to level of impact (e.g., individual, couple, family, community, or broader social attitudes toward LGBTQ+ individuals; see S1 Table). A final category on significance/implications allowed reviewers to further identify and comment on major themes and relevance to the current review. Themes were then identified and organized using stigma and social-ecological frameworks.

Individual level impacts.
Although most studies about the impact of equal marriage rights have been conducted with couples or individuals in committed or married relationships, 15 studies in this review included sexual minority adults across relationship statuses. In general, studies examining the impact of equal marriage rights among sexual minorities suggest that equal access to marriage has a positive impact on perceptions of social acceptance and social inclusion regardless of relationship status [47, 63,66,67]. For example, Riggle and colleagues [47] examined perceptions of sexual minority individuals in the U.S. during the period in which same-sex couples had equal marriage rights in some, but not all, U.S. states. Sexual minorities who resided in states with equal marriage rights reported less identity concealment, vigilance, and isolation than their peers in states without equal marriage rights. Similarly, using data from the longitudinal Nurses' Health Study in the U.S., Charlton and colleagues [68] examined potential positive impacts of equal marriage rights on sexual identity disclosure. They found that participants living in states with any form of legal recognition of same-sex relationships (inclusive of marriage, civil unions, or domestic partnerships) were 30% more likely than those is states without legal recognition to consistently disclose a sexual minority identity across survey waves [68].
Researchers have documented ambivalence among sexual minority adults regarding the institution of marriage and whether same-sex marriage would impact other forms of structural or interpersonal stigma. Sexual minority participants in several studies expressed concern about continued interpersonal stigma based on sexual or gender identity, the limitations of marriage as a vehicle for providing benefits and protections for economically marginalized LGBTQ+ individuals, and the possibility that an increased focus on marriage would contribute to devaluing unmarried same-sex relationships [12,13,62,69,70]. Studies also documented concerns about marriage being inherently linked to heteronormative expectations and about assimilation to heterosexist cultural norms [60,69,71]. These concerns were summarized by Hull [69]: "The fact that LGBTQ respondents favor marriage more in principle (as a right) than in practice (as an actual social institution) suggests that marriage holds multiple meanings for them" (p. 1360).
Five studies explicitly examined racial/ethnic minority identities as a factor in individuals' perceptions of same-sex marriage; one qualitative study focused exclusively on Black individuals in the U.S. [72] and the other four examined differences by race/ethnicity [64,66,67,73].
McGuffy [72] conducted in-depth interviews with 102 Black LGBT individuals about their perceptions of marriage as a civil rights issue before and after same-sex marriage was recognized nationally in the U.S. The study found that intersecting identities and experiences of discrimination related to racism, homophobia, and transphobia influenced personal views of marriage. For example, although most participants were supportive of equal marriage rights as a public good, many felt that the emphasis on marriage in social movement efforts overlooked other important issues, such as racism, economic injustice, and transgender marginalization.
The four other studies examining racial/ethnic differences in perceptions about whether equal marriage rights facilitated inclusion or reduced interpersonal stigma yielded mixed results. One found that residing in states with equal marriage rights was associated with greater feelings of acceptance among sexual minorities; however, White sexual minorities reported greater feelings of inclusion than participants of color [66]. By contrast, in a quasi-experiment in which SMW in a midwestern state were interviewed pre-or post-passage of civil union legislation, those interviewed after the legislation reported lower levels of stigma consciousness and perceived discrimination than those interviewed before the legislation; however, effects were stronger among SMW of color than among White SMW [64]. In a study of unmarried men in same-sex male couples, Hispanic/Latino men were more likely than non-Latino White participants to report perceived gains in social inclusion after equal marriage rights were extended to all U.S. states [67]. However, men who reported higher levels of minority stress (enacted and anticipated stigma as well as internalized homophobia) were less likely to show improvement in perceptions of social inclusion. Lee [73], using data from a national Social Justice Sexuality Project survey, found no statistical differences in Black, White and Latinx sexual minorities' perceptions that equal marriage rights for same-sex couples had a moderate to major impact on their lives. In analyses restricted to Black participants, individuals with higher level of sexual minority identity salience reported significantly higher importance of equal marriage rights. Lee suggests that same-sex marriage was perceived by many study participants as a tool to gain greater acceptance in the Black community because being married is a valued social status.
Couple level impacts. We identified 15 studies that focused on couples as the unit of analysis. Findings from studies of the extension of equal marriage rights in U.S. states suggest positive impacts among same-sex couples, including access to financial and legal benefits as well as interpersonal validation, such as perceptions of being viewed as a "real" couple and increased social inclusion [12,59,63,74,75]. Furthermore, couples in several studies described the potential positive impacts of legal recognition of their relationship on their ability to make joint decisions about life issues, such as having children and medical care [75]. Couples also described having a greater sense of security associated with financial (e.g., taxes, healthcare) and legal (e.g., hospital visitation) benefits and reduced stress in areas such as travel and immigration [75]. Collectively, these findings suggest that marriage rights were perceived to imbue individuals in same-sex relationships with a sense of greater security, stability, and safety due to the legal recognition and social legitimization of same-sex couples. Although equal marriage rights were perceived as an important milestone in obtaining civil rights and reducing institutional discrimination, concerns about and experiences of interpersonal stigma persisted [76][77][78]. The social context of legal same-sex marriage may create stress for couples who elect to not marry. For example, in a study of 27 committed, unmarried same-sex couples interviewed after the U.S. Supreme Court decision on Obergefell, couples who chose not to marry described feeling that their relationships were less supported and perceived as less committed [79].
Reports from the CUPPLES study, a national longitudinal study of same-sex couples in the U.S. from 2001 to 2014, provided a unique opportunity to examine the impact of different forms of legal recognition of same-sex relationships. In wave three of the study during 2013-2014, open-ended qualitative questions were added to explore how individuals in long-term committed partnerships perceived the extension of equal marriage rights in many U.S. states. Themes included awe about the historic achievement of a long-awaited civil rights goal, celebration and elation, and affirmation of minority sexual identity and relationships, but also fears of backlash against sexual minority rights [80]. Some individuals who divorced after institutionalization of the right to same-sex marriage reported shame, guilt, and disappointmentgiven that they and others had fought so hard for equal marriage rights [81].
Studies outside the U.S. have also found evidence of positive impacts of legal recognition of same-sex couple relationships (e.g., increased social recognition and social support), as well as potential concerns [82][83][84][85][86]. For example, in a study of couples from the first cohort of samesex couples to legally marry in Canada, participants described marriage as providing them with language to describe their partner that was more socially understood and helping to decrease homophobic attitudes among the people around them [83]. Some couples said they could fully participate in society and that marriage normalized their lives and allowed them to "live more publicly." Couples also discussed the safety, security, and increased commitment that came from marriage, and some felt that marriage opened up previously unavailable or unimagined opportunities, such as becoming parents. However, some participants noted that their marriage caused disjuncture in relationships with their family of origin, as marriage made the relationship feel too real to family members and made their sexual identities more publicly visible.
Family level impacts. Seventeen studies examined the impact of equal marriage rights on sexual minority individuals' or couples' relationships with their families of origin. Although these studies predominately used cross-sectional survey designs, one longitudinal study included individuals in both different-sex and same-sex relationships before and after the U.S. Supreme Court decision that extended marriage rights to all states [44]. This study found that support from family members increased following national legalization of same-sex marriage [44]. A cross-sectional online survey of 556 individuals with same-sex partners in Massachusetts (the first U.S. state to extend equal marriage rights to same-sex couples), found that greater family support and acceptance of same-sex couples who married was associated with a stronger overall sense of social acceptance [66].
Other cross-sectional surveys found mixed perceptions of family support and feelings of social acceptance. For example, a study of 357 participants in long-term same-sex relationships found that perceived social support from family did not vary by state-level marriage rights or marital status [47]. However, living in a state with same-sex marriage rights was associated with feeling less isolated. The finding of no differences in perceived support might be partly explained by the fact that the sample included only couples in long-term relationships; older, long-term couples may rely less on support from their family of origin than younger couples [12].
In studies (n = 6) that included dyadic interviews with same-sex married couples [74,79,85,[87][88][89], participants described a wide range of family members' reactions to their marriage. These reactions, which emerged after same-sex marriage legalization, were typically described by couples as profoundly impactful. Couples who perceived increased family support and acceptance described these changes as triumphant [85], transformative [88], and validating [74,87]. Conversely, some same-sex couples reported feeling hurt and betrayed when familial reactions were negative or when reactions among family members were divided [85,87,89]. Findings from these and other studies suggest that if certain family members were accepting or rejecting prior to marriage, they tended to remain so after equal marriage rights and/or the couple's marriage [61,74,90,91]. In some cases, family members were perceived as tolerating the same-sex relationship but disapproving of same-sex marriage [85,90].
Findings from studies of married sexual minority people suggest that family (especially parental) disapproval was a challenge in the decision to get married [92], possibly because disclosure of marriage plans by same-sex couples frequently disrupted family "privacy rules" and long-time patterns of sexual identity concealment within families or social networks [87]. In a few studies, same-sex partners perceived that their marriage gave their relationship more legitimacy in the eyes of some family members, leading to increased support and inclusion [61,66,[89][90][91]. Further, findings from two studies suggested that participating in same-sex weddings gave family members the opportunity to demonstrate support and solidarity [87,93].
Two qualitative studies collected data from family members of same-sex couples. In one, heterosexual siblings (all of whom were in different-sex marriages) described a range of reactions to marriage equality-from support for equal marriage rights to disapproval [80]. The other study interviewed sexual minority migrants to sexual minority friendly countries in Europe who were married and/or raising children with a same-sex partner, and these migrant's parents who lived in Central and Eastern European countries that prohibited samesex marriage. Parents found it difficult to accept their adult child's same-sex marriage, but the presence of grandchildren helped to facilitate acceptance [94].
Community level impacts. Twelve studies in this review examined the community-level impacts of same-sex marriage. These studies focused on community level impacts from two perspectives: impacts of equal marriage rights on LGBTQ+ communities, and the impacts of equal marriage rights on LGBTQ+ individuals' interactions with their local communities or extended social networks.
LGBTQ+ communities. A prominent theme among these studies was that marriage is beneficial to LGBTQ+ communities because it provides greater protection, recognition, and acceptance of sexual minorities, their families, and their relationships-even beyond the immediate impact on any individual and their relationship or marriage [12,62,89,95]. Despite these perceived benefits, studies have found that some sexual minority adults view marriage as potentially harmful to LGBTQ+ communities because of concerns about increased assimilation and mainstreaming of LGBTQ+ identities [12,50,62], stigmatizing unmarried relationships [62], and weakening of unique and valued strengths of LGBTQ+ culture [12]. For example, Bernstein, Harvey, and Naples [96] interviewed 52 Australian LGBTQ+ activists and legislators who worked alongside activists for equal marriage rights. These authors described the "assimilationist dilemma" faced by activists: a concern that gaining acceptance into the mainstream societal institution of marriage would lessen the salience of LGBTQ+ identity and ultimately diminish the richness and strength of LGBTQ+ communities. Another downside of the focus on marriage as a social movement goal was the concern about reinforcing negative heteronormative aspects of marriage rather than challenging them [95].
Four studies explicitly examined possible community level impacts of same-sex marriage. In a mixed-methods study with 115 LGBTQ+ individuals in Massachusetts, participants reported believing that increased acceptance and social inclusion as a result of equal marriage rights might lessen reliance on LGBTQ+-specific activism, events, activities, and venues for social support [13]. However, a majority of study participants (60%) reported participating in LGBTQ+-specific events, activities, or venues "regularly." A few studies found evidence of concerns that the right to marry could result in marriage being more valued than other relationship configurations [12,62,79].
Local community contexts and extended social networks. Studies examining the impact of same-sex marriage on sexual minority individuals' interactions with their extended social networks and in local community contexts yielded mixed results. In an interview study with 19 same-sex couples living in the Netherlands, Badgett [66] found that LGBTQ+ people experienced both direct and indirect increases in social inclusion in their communities and extended social networks as a result of equal marriage rights. For example, direct increases in social inclusion included people making supportive comments to the couple and attending their marriage ceremonies; examples of indirect increases included same-sex spouses being incorporated into family networks [66]. Other studies found mixed or no change in support for LGBTQ+ people and their relationships. Kennedy, Dalla, and Dreesman [61] collected survey data from 210 married LGBTQ+ individuals in midwestern U.S. states, half of whom were living in states with equal marriage rights at the time of data collection. Most participants did not perceive any change in support from their community/social network following legalization of same-sex marriage; other participants reported an increase or mixed support from friends and co-workers. Similarly, Wootton and colleagues interviewed 20 SMW from 15 U.S. states and found positive, neutral, and negative impacts of same-sex marriage on their interactions in work and community contexts [50]. Participants perceived increased positivity about LGBTQ + issues and more accepting attitudes within their extended social networks and local communities, but also reported hearing negative comments about sexual minority people more frequently and experiencing continued sexual orientation-based discrimination and stigma [50]. Many SMW reported feeling safer and having more positive conversations after Obergefell, but also continued to have concerns about being out at work as a sexual minority person [50].
Two studies examined the experiences of LGBTQ+ people in U.S. states in which same-sex marriage restrictions were decided by voters through ballot measures. These studies documented mixed impacts on participants' interactions with extended social networks and community. Maisel and Fingerhut [28] surveyed 354 sexual minority adults in California immediately before the vote to restrict recognition of marriage to one man and one woman in the state (Proposition 8) and found that about one-third experienced interactions with social network members that were positive, whereas just under one-third were negative, and the rest were either mixed or neutral. Overall, sexual minority people reported more support than conflict with extended social network members and heterosexual community members over the ballot measure, with friends providing the most support [28]. Social support and solidarity from extended social network members in the face of ballot measures to restrict marriage recognition were also reported in an interview study of 57 same-sex couples residing in one of seven U.S. states that had passed marriage restriction amendments in 2006 [97]. However, some LGBTQ+ people also experienced condemnation and avoidance in their extended social networks [97].

Societal level impacts.
Sixteen studies examined ways that same-sex marriage influenced societal attitudes about sexual minority individuals or contributed to additional shifts in policies protecting the rights of sexual minority individuals. Findings suggested that the right of same-sex couples to marry had a positive influence on the political and socio-cultural context of sexual minorities' lives. For example, changes in laws may influence social attitudes or result in LGBTQ positive policy diffusion across states (jurisdictions). There is debate over whether legal changes, such as equal marriage rights, create or are simply reflective of changes in social attitudes toward a group or a social issue [98]. Flores and Barclay [98] theorize four different socio-political responses to changes in marriage laws: backlash, legitimacy, polarization, and consensus. Some scholars argue that changes in law are unlikely to impact social attitudes (consensus), while others argue that legal changes influence the political and social environment that shapes social attitudes. Possible effects range from decreased support for sexual minorities and attempts to rescind rights (backlash) to greater support for the rights of sexual minorities and possible future expansion of rights and protections (legitimacy).
Findings from research generally suggest a positive relationship between same-sex marriage and public support for the overall rights of sexual minorities (legitimacy), and mixed results related to changes in mass attitudes (consensus) [98][99][100][101][102][103][104][105][106]. For example, in a panel study in Iowa before and after a state Supreme Court ruling in favor of equal marriage rights, Kreitzer and colleagues found that the change in law modified registered voters' views of the legitimacy of samesex marriage and that some respondents felt "pressure" to modify or increase their expressed support [102]. Similarly, Flores and Barclay [98] found that people in a state with equal marriage rights showed a greater reduction in anti-gay attitudes than people in a state without equal marriage rights. Studies based on data from European countries also found that more positive attitudes toward sexual minorities were associated with equal marriage rights; improvements in attitudes were not evident in countries without equal marriage rights [9,105,106].
There is some evidence to support the third possible socio-political response to changes in marriage laws in Flores and Barclay's model: increased polarization of the general public's attitudes toward sexual minorities. Perrin, Smith, and colleagues [107], using successive-independent samples study of conservatives, moderates, and progressives across the U.S. found no overall changes in opinions attitudes about sexual minorities immediately after the Supreme Court decision extending equal marriage rights to all same-sex couples in the U.S. However, analyses by subgroup found that those who were conservative expressed more prejudice toward gay men and lesbians, less support for same-sex marriage, and less support for LGB civil rights immediately after the decision. Similarly, drawing on data from approximately one million respondents in the U.S. who completed implicit and explicit measures of bias against gay men and lesbian women (Project Implicit), Ofosu and colleagues [100] found that implicit bias decreased sharply following Obergefell. However, changes in attitudes were moderated by state laws; respondents in states that already had equal marriage rights for same-sex couples demonstrated decreased bias whereas respondents in states that did not yet have equal marriage rights evidenced increased bias [100]. Using data from the World Values Survey  in European countries, Redman [103] found that equal marriage rights were associated with increases in positive opinions about sexual minorities, but that the increase was driven largely by those who already held positive views.
Little support has been found for the hypothesis that the extension of equal marriage rights would be followed by a backlash of sharp negative shifts in mass attitudes and public policy [98,108,109]. For example, a general population survey in one relatively conservative U.S. state (Nebraska) found public support for same-sex marriage was higher after the Supreme Court ruling than before, suggesting no backlash in public opinion [108]. Similarly, Bishin and colleagues [109], using both an online survey experiment and analysis of data from a U.S. public opinion poll (National Annenberg Election Studies) before and after three relevant policy events, found little change in public opinion in response to simulated or actual policy changes.
Although equal marriage rights confer parental recognition rights, there are still legal challenges and disparate rulings and interpretations about some family law issues [77,110,111]. For example, some states in the U.S. have treated the parental rights of same-sex couples differently than those of different-sex (presumed heterosexual) couples. Both members of a samesex couple have traditionally not been automatically recognized as parents of a child born or adopted within the relationship. However, the presumptions of parenthood after same-sex marriage was legalized have forced states to treat both members of same-sex couples as parents irrespective of method of conception or adoption status [112]. Still, results from a crossnational study of laws, policies, and legal recognition of same-sex relationships suggests that parental rights are recognized in some jurisdictions but not others [111].

Aim 2: SMW-specific findings and differences by gender
A total of 13 studies included in this review conducted SMW-specific analyses or compared SMW and SMM's perceptions and experiences of same-sex marriage and equal marriage rights. In studies that included only SMW [50, 64,68,77,81,86,89,91], findings emphasized the importance of relational and interpersonal impacts of same-sex marriage. Examples include creating safety for sexual identity disclosure and visibility [68,81], providing legal protections in relation to partners and/or children [77,81], offering social validation [86,89], and reducing stigma in larger community contexts [50,64]. Relational themes centered on concerns and distress when experiencing rejection or absence of support from family members or extended social networks [50, 81,86,89,91].
Two of the studies of SMW documented sexual identity and gender identity differences in interpersonal experiences associated with same-sex marriage [86,89]. Lannutti's interview study of the experiences of 26 married or engaged SMW couples with different sexual identities (bisexual-lesbian couples) revealed how the right to marry made them feel more connected to LGBTQ+ communities through activism and being "counted" as a same-sex married couple. However, same-sex marriage made some bisexual women feel more invisible within LGBTQ+ communities [89]. Scott and Theron [86] found that married lesbian women and cisgender women partners of transmasculine individuals (i.e., masculine-identifying transgender individuals) faced different challenges as they navigated through gendered social expectations and made choices about conforming or rejecting heteronormativity.
Only five of the studies focusing on psychosocial impacts of equal marriage rights explicitly examined potential differences by sex [28,66,73,76,95]. Some studies found perceptions of greater social inclusion [66], or feelings of ambivalence (simultaneously holding positive, negative, and critical perspectives about marriage as an institution) [95] that were similar among SMW and SMM. Maisel and Fingerhut's study of consequences of a state-level campaign to restrict marriage rights [28] showed that SMW and SMM experienced similar negative impacts on personal well-being and interactions with extended social networks. However, Lee found that, compared with Black SMM, Black SMW perceived same-sex marriage to have a larger impact on their lives [73]. Other studies found that SMW were more likely than SMM to report positive perceptions of same-sex marriage, possibly because they are more likely than SMM to have children and to be concerned about parental protections [73,95]. SMW and SMM may be differentially impacted by interpersonal stigma despite equal marriage rights. For example, one study found that SMW experienced higher levels of distress than SMM when their relationships were not treated as equal to heterosexuals' [76].

Discussion
Overall, findings from this scoping review suggest that psychosocial impacts of equal marriage rights among sexual minorities are apparent at all levels of our social-ecological and stigma framework. Sexual minority-specific stigma occurs on multiple levels (e.g., individual, interpersonal, and structural simultaneously and changes in social policies have cascading effects on sexual minority individuals' experiences at each level. Generally, equal marriage rights had a positive impact on perceptions of social acceptance and social inclusion for sexual minority individuals, couples, and the LGBTQ+ community as a whole. However, many studies described mixed, ambivalent, or complicated perceptions of samesex marriage, as well as stigmatizing interactions that were unaffected or exacerbated by equal marriage rights. Although research does not unequivocally suggest the presence of a backlash in public opinion after equal marriage rights, there has been an increase in laws and policies at the U.S. state and federal levels that explicitly allow for religious-belief-based denial of services to sexual minority individuals and same-sex couples. For example, by 2017, 12 states in the U.S. enacted laws permitting the denial of services (e.g., allowing government officials to refuse to issue same-sex marriage licenses, allowing magistrates to refuse to perform same-sex marriages, and permitting adoption and child welfare agencies to refuse same-sex couples' adoption or fostering children) based on religious beliefs [113]. Research has documented negative health and psychological outcomes among sexual minorities living in U.S. states with policies that permit denial of services to sexual or gender minorities [114,115] and in states that do not have legal protections against discrimination [38,116,117]. Additional research is needed to examine how changes in local or national laws impact the health and well-being of sexual and gender minorities-particularly over the long term.

Gaps & future research needs
Research is limited in terms of examining how same-sex marriage may differentially impact sexual minority individuals based on sex, gender identity, or race/ethnicity. Only 14 studies included in this review addressed the psychosocial impacts of same-sex marriage among SMW. More research is needed to understand the unique experiences and psychosocial impact of same-sex marriage for SMW and SMM. Further, many study samples were largely homogenous and included an overwhelming majority of White participants. The few studies with substantial sample sizes of people of color, and that compared people of color to White people, found differences by race in perceived impact of same-sex marriage [64,67,73], demonstrating the need for additional work in this area.
There were also very few studies in this review that explored differences by sexual identity (e.g., monosexual vs. plurisexual), gender identity (e.g., transgender vs. cisgender), gender expression (e.g., masculine vs. feminine presentation), or differences based on sex/gender of participants' partners. Although transgender and nonbinary individuals were included in eight studies, five provided only descriptive information and only three described any unique findings from transgender study participants. For example, McGuffey [72] found that transgender individuals who identified as heterosexual described same-sex marriage rights as less relevant than issues of gender identity and expression and Hull found that cisgender sexual minority men generally expressed more enthusiasm about marriage than both cisgender women and transgender individuals [69]. Transgender and nonbinary individuals who perceive positive impacts of equal marriage rights may still experience challenges in navigating heteronormative and cisnormative expectations [72,86]. Other qualitative studies documented concerns that LGBTQ+ advocacy efforts, once marriage rights were secured, might fail to address rights and protections for transgender and nonbinary individuals [62,69]. Future studies that include the voices of transgender and nonbinary individuals are needed to better understand perceptions across both sexual and gender identities [118].
There is limited research on immediate and extended family members' perceptions of equal marriage rights. There is also a need for prospective studies that examine whether familial acceptance increases over time. Many studies did not account for differences in LGBTQ+ identity salience and connection to LGBTQ+ and other communities, which may influence differences in perceptions and reactions to same-sex marriage.
The majority of studies (43 of 59) we reviewed were conducted in the U.S. Eleven of these collected data after Obergefell (June 25, 2015). Only two used longitudinal research designs that included data collection before and after national same-sex marriage legalization [44,107]. The legal and social landscapes have changed since this time and there is a need for reassessment of the impact of same-sex marriage over multiple future timepoints.

Limitations
Although this scoping review used a systematic approach and, to our knowledge, is novel in its focus on impact of equal marriage rights on sexual minorities' personal lives, interpersonal relationships, and social/community contexts, we acknowledge several limitations. We did not conduct a search of grey literature (e.g., reports, policy literature, working papers) or books and, consequently, likely excluded some scholarly work aligned with our focus. Our inclusion criteria of only peer-reviewed studies may have led us to exclude dissertations that focus on emerging areas of research, such as differences by gender identity, sexual identity, or race and ethnicity. As with all scoping reviews, studies may have been missed because of the search strategy. For example, it is possible that relevant studies were indexed in databases not used in our review. We also restricted our review to English language literature, excluding potentially relevant studies published in other languages. Studies in other languages may provide useful insights from other countries where English is not widely used. Although we focused exclusively on empirical studies, we did not assess the quality of the studies. Findings of the review are also limited by the collective body of research questions, designs, and analyses that have been pursued. For example, as noted above, few studies explored psychosocial impacts of same-sex marriage among SMW or explored differences by sex; consequently we were limited in our ability to address our second research aim.

Conclusion
This scoping review identified and described psychosocial impacts of equal marriage rights among sexual minority adults and explored potential SMW-specific experiences and differences by sex. Our results highlight four points. First, equal marriage rights are associated with a wide range of positive impacts on the psychological and social well-being of sexual minority adults. Second, the potential positive impacts of equal marriage rights are amplified or weakened by the presence or absence of stigma in interpersonal interactions and in the larger political and social environment. Third, although there is a growing body of global research on the impact of same-sex marriage, most studies have been conducted in the U.S. Cross-cultural studies can improve understanding of individual, interpersonal, and community level impacts of same-sex marriage in different cultural contexts. Fourth, given indications of differences between SMW and SMM in perceived impact of same-sex marriage, there is a need for research that examines the specific perspectives of SMW and that explores possible differences in perspectives and experiences by sex. Research is also needed to understand differences based on race/ethnicity, gender identity, and age. The right of same-sex couples to marry does not merely address the concerns of sexual minorities, it aims to right a far bigger wrong: the exclusion of some individuals from one of the most important institutions in social life.
Supporting information S1 Table. Articles included in scoping review on the psychosocial impact of equal marriage rights among sexual minority adults. (PDF) S1 Checklist. Preferred Reporting Items for Systematic reviews and Meta-Analyses extension for scoping reviews (PRISMA-ScR) checklist.