The Socioecology of Sexual Minority Stigma: Data Harmonization to Address Confounding Bias and Investigate Cross-Level MentalHealth Effects - PROJECT SUMMARY/ABSTRACT Sexual minorities (i.e., individuals who do not identify as heterosexual, or who are attracted to, have romantic relationships with, or have sexual contact with, people of the same or diverse genders) in the US are at a near three-fold increased odds for depression and a two to seven-fold increased risk for lifetime report of suicide attempts, compared with heterosexual individuals. Structural sexual minority stigma exposure across various levels (e.g., macro and exo levels) has been purported as a cause underlying and driving these sexual orientation-based disparities in mental health. While structural forms of sexual minority stigma, including discriminatory laws, inequitable policies, and negative population attitudes, have been associated with adverse sexual minority mental health, evidence from US-based studies, depending on single stand-alone indicators of structural stigma, has been hampered by risks for confounding bias through common causes from other 1) higher-level and 2) same-level structural stigma-related factors, as well as 3) often-overlooked structural factors outside of the stigma paradigm. Large existing US public health surveys do not independently allow for analyses that can fully account for such confounding bias. But data harmonization and integration across datasets (i.e., NHIS, Add Health, YRBS, and ABCD) will enable complex models with newly developed comprehensive macro- (i.e., state) and exo-level (i.e., county) structural sexual minority stigma predictors of individual-level mental health outcomes, sufficient clusters, and large-enough mean cluster sizes. With data collected during a transformational period for sexual minorities in the US (from 2001 to 2021; e.g., changes in population attitudes and the step-wise introduction of same-gender marriage), the NHIS, Add Health, YRBS, and ABCD, together, provide a once-in-a-generation and timely opportunity to harmonize and integrate these datasets to enable complex multilevel models that account for the risks of confounding bias and aid to further strengthen causal inferencing. Therefore, this proposed study will 1) harmonize and pool high-quality data from up to 42,000 sexual minority and 1.4 million heterosexual individuals, 2) comprehensively quantify the level of structural sexual minority stigma exposure in US states and counties between 2001 and 2021, and 3) examine the cross-sectional and longitudinal associations between cross-level (i.e., macro to exo) effects of structural sexual minority stigma and depressive symptoms and suicidality outcomes (namely, suicidal ideation and suicidal behaviors). Findings from the proposed study may have direct theoretical and applied implications as it addresses important confounding issues currently distorting findings on how macro- and exo-level structural sexual minority stigma shape sexual minorities’ mental health. Results may further contribute to health equity by facilitating targeted advocacy and therapeutic interventions to improve structural climates for sexual minorities and combat systemic effects, not only in the US, but similarly across the globe.