Trang Q. Nguyen

Johns Hopkins Bloomberg School of Public Health | JHSPH · Department of Mental Health

Purpose: Disapproval of homosexuality is the cause of tremendous suffering among sexual minorities. No research has examined determinants of Vietnamese attitudes toward homosexuality. This article examined predictors of such attitudes among Vietnamese youth. Methods: Data were from Vietnamese youth aged 15–24 years nationally surveyed in 2009 (Surv...

To examine whether increasing investment in needle/syringe exchange programs (NSPs) in the US would be cost-effective for HIV prevention, we modeled HIV incidence in hypothetical cases with higher NSP syringe supply than current levels, and estimated number of infections averted, cost per infection averted, treatment costs saved, and financial retu...

Quantitative research on parental/family disapproval and rejection of sexual/gender minority persons has often measured family rejection as one binary/continuous variable, or using several variables representing specific behaviors or dimensions of behaviors. Absent from this literature is analysis using a person-oriented approach, examining heterog...

Understanding and addressing heterosexual HIV transmission requires attention to the range and context of heterosexual sexual behaviors. We sought to determine population-based prevalence of condomless anal intercourse (CAI) among individuals at increased heterosexual HIV risk in Baltimore and to identify demographic, behavioral, and health-related...

Missing data is a common problem that challenges the study of effects of treatments. In the context of mediation analysis, this paper addresses missingness in the two key variables, mediator and outcome, focusing on identification. We consider self-separated missingness models where identification is achieved by conditional independence assumptions...

This paper concerns outcome missingness in principal stratification analysis. We revisit a common assumption known as latent ignorability or latent missing-at-random (LMAR), often considered a relaxation of missing-at-random (MAR). LMAR posits that the outcome is independent of its missingness if one conditions on principal stratum (which is partia...

Aims The aim of this study was to measure trajectories of craving for methamphetamine during the course of pharmacotherapy trials for methamphetamine use disorder. Design, setting and participants Craving trajectories were identified using Group‐Based Trajectory Modeling. The association of craving trajectories with drug use trajectories was exami...

An important strategy for identifying principal causal effects (popular estimands in settings with noncompliance) is to invoke the principal ignorability (PI) assumption. As PI is untestable, it is important to gauge how sensitive effect estimates are to its violation. We focus on this task for the common one‐sided noncompliance setting where there...

In epidemiology and social sciences, propensity score methods are popular for estimating treatment effects using observational data, and multiple imputation is popular for handling covariate missingness. However, how to appropriately use multiple imputation for propensity score analysis is not completely clear. This paper aims to bring clarity on t...

Mediation analysis is a statistical approach that can provide insights regarding the intermediary processes by which an intervention or exposure affects a given outcome. Mediation analyses rose to prominence, particularly in social science research, with the publication of Baron and Kenny’s seminal paper and is now commonly applied in many research...

The study of treatment effects is often complicated by noncompliance and missing data. In the one-sided noncompliance setting where of interest are the complier and noncomplier average causal effects, we address outcome missingness of the latent missing at random type (LMAR, also known as latent ignorability). That is, conditional on covariates and...

The relationships between place (e.g., neighborhood) and HIV are commonly investigated. As measurements of place are multivariate, most studies apply some dimension reduction, resulting in one variable (or a small number of variables), which is then used to characterize place. Typical dimension reduction methods seek to capture the most variance of...

Individualized treatment decisions can improve health outcomes, but using data to make these decisions in a reliable, precise, and generalizable way is challenging with a single dataset. Leveraging multiple randomized controlled trials allows for the combination of datasets with unconfounded treatment assignment to better estimate heterogeneous tre...

The choice of which covariates to adjust for (so-called allowability designation) in health disparity measurements reflects value judgements about inequitable versus equitable sources of health differences, which is paramount for making inferences about disparity. Yet, many off-the-shelf estimators used in health disparity research are not designed...

Individualized treatment decisions can improve health outcomes, but using data to make these decisions in a reliable, precise, and generalizable way is challenging with a single dataset. Leveraging multiple randomized controlled trials allows for the combination of datasets with unconfounded treatment assignment to improve the power to estimate het...

An important strategy for identifying principal causal effects, which are often used in settings with noncompliance, is to invoke the principal ignorability (PI) assumption. As PI is untestable, it is important to gauge how sensitive effect estimates are to its violation. We focus on this task for the common one-sided noncompliance setting where th...

Background: Transgender and gender non-binary (TNB) people have been disproportionately impacted by HIV and the COVID-19 pandemic. This study explored the prevalence of HIV prevention and treatment (HPT) interruptions during the pandemic and identified factors associated with these interruptions. Setting: Data were drawn from LITE Connect, a U.S...

Estimating treatment effects conditional on observed covariates can improve the ability to tailor treatments to particular individuals. Doing so effectively requires dealing with potential confounding, and also enough data to adequately estimate effect moderation. A recent influx of work has looked into estimating treatment effect heterogeneity usi...

In epidemiology and social sciences, propensity score methods are popular for estimating treatment effects using observational data, and multiple imputation is popular for handling covariate missingness. However, how to appropriately use multiple imputation for propensity score analysis is not completely clear. This paper aims to bring clarity on t...

Causal mediation analysis is complicated with multiple effect definitions that require different sets of assumptions for identification. This article provides a systematic explanation of such assumptions. We define five potential outcome types whose means are involved in various effect definitions. We tackle their mean/distribution’s identification...

Existing studies have suggested superior performance of nonparametric machine learning over logistic regression for propensity score estimation. However, it is unclear whether the advantages of nonparametric propensity score modeling are carried to settings where there is clustering of individuals, especially when there is unmeasured cluster‐level...

Mediation analysis aims to investigate the “mechanisms of action” behind the effects of interventions or treatments. Originally developed in psychology, a robust set of mediation methods are now used across a range of fields. Given the history and common use of mediation in mental health research, this review aimed to understand how mediation analy...

Causal inference analyses often use existing observational data, which in many cases has some clustering of individuals. In this paper, we discuss propensity score weighting methods in a multilevel setting where within clusters individuals share unmeasured confounders that are related to treatment assignment and the potential outcomes. We focus in...

This paper aims to contribute to helping practitioners of causal mediation analysis gain a better understanding of estimation options. We take as inputs two familiar strategies (weighting and model-based prediction) and a simple way of combining them (weighted models), and show how we can generate a range of estimators with different modeling requi...

Literature on health-related quality of life (HRQOL) has focused on people living with chronic conditions, with less attention given to HRQOL among informal caregivers. We used cross-sectional dyadic data from both care recipients (CR) living with HIV and the person they identified as their primary informal (unpaid) caregiver (CG) to identify psych...

Inflammation is an emerging risk factor for prostate cancer based largely on evidence from animal models and histopathologic observations. However, findings from patho-epidemiologic studies of intraprostatic inflammation and prostate cancer have been less supportive, with inverse associations observed in many studies of intraprostatic inflammation...

Background: Randomized controlled trials are often used to inform policy and practice for broad populations. The average treatment effect (ATE) for a target population, however, may be different from the ATE observed in a trial if there are effect modifiers whose distribution in the target population is different that from that in the trial. Method...

Causal mediation analysis is complicated with multiple effect definitions that require different sets of assumptions for identification. This paper provides a systematic explanation of such assumptions. We define five potential outcome types whose means are involved in various effect definitions. We tackle their mean/distribution's identification,...

The incorporation of causal inference in mediation analysis has led to theoretical and methodological advancements-effect definitions with causal interpretation, clarification of assumptions required for effect identification, and an expanding array of options for effect estimation. However, the literature on these results is fast-growing and compl...

We address measurement error bias in propensity score (PS) analysis due to covariates that are latent variables. In the setting where latent covariate X is measured via multiple error-prone items W, PS analysis using several proxies for X—the W items themselves, a summary score (mean/sum of the items), or the conventional factor score (i.e., predic...

Policymakers use results from randomized controlled trials to inform decisions about whether to implement treatments in target populations. Various methods—including inverse probability weighting, outcome modeling, and Targeted Maximum Likelihood Estimation—that use baseline data available in both the trial and target population have been proposed...

Background Many studies in psychological and educational research aim to estimate population average treatment effects (PATE) using data from large complex survey samples, and many of these studies use propensity score methods. Recent advances have investigated how to incorporate survey weights with propensity score methods. However, to this point,...

Causal inference analyses often use existing observational data, which in many cases has some clustering of individuals. In this paper we discuss propensity score weighting methods in a multilevel setting where within clusters individuals share unmeasured variables that are related to treatment assignment and the potential outcomes. We focus in par...

We address measurement error bias in propensity score (PS) analysis due to covariates that are latent variables. In the setting where latent covariate $X$ is measured via multiple error-prone items $\mathbf{W}$, PS analysis using several proxies for $X$ -- the $\mathbf{W}$ items themselves, a summary score (mean/sum of the items), or the convention...

The incorporation of causal inference in mediation analysis has led to theoretical and methodological advancements -- effect definitions with causal interpretation, clarification of assumptions required for effect identification, and an expanding array of options for effect estimation. However, the literature on these results is fast-growing and co...

Background: Current models of HIV prevention intervention dissemination involve packaging interventions developed in one context and training providers to implement that specific intervention with fidelity. Providers rarely implement these programs with fidelity due to perceived incompatibility, resource constraints, and preference for locally-gen...

Suppose we are interested in the effect of variable X on variable Y . If X and Y both influence, or are associated with variables that influence, a common outcome, called a collider , then conditioning on the collider (or on a variable influenced by the collider – its “child”) induces a spurious association between X and Y , which is known as colli...

Background Randomized controlled trials are often used to inform policy and practice for broad populations. The average treatment effect (ATE) for a target population, however, may be different from the ATE observed in a trial if there are effect modifiers whose distribution in the target population is different that from that in the trial. Methods...

Additional details on extension 1 for random intercepts models. (PDF)

Illustration—Trial data. (CSV)

Additional details on the case of effect modifiers not observed in the trial. (PDF)

Illustration—Main appendix with explanations and most of the code in R (read this before S7-9). (HTML)

Illustration—Stata code for fitting random effects models with probability weights. (DO)

Illustration—Target population data. (CSV)

An explanation of why the different weighting procedures apply in the different data scenarios. (PDF)

Additional details on extension 2 for multiplicative effects and log/logit link models. (PDF)

Evidence indicates that social cohesion is a successful strategy to improve consistent condom use (CCU) among female sex workers. However, the individual and layered or combined effect that various types of overlapping stigmas may have on CCU between female sex workers living with HIV and their clients and steady partners has not been analyzed. Dra...

Malawi is one of 14 priority countries for voluntary medical male circumcision (VMMC) initiatives with the lowest VMMC uptake. Using data from a study of 269 men accessing VMMC in southern Malawi and latent class analysis, men were classified based on four risk factors: ever tested for HIV, condom use at last sex, having casual/concurrent sexual pa...

Given the declining trend in adolescent cigarette smoking and increase in general access to marijuana, it is important to examine whether marijuana use in adolescence is a risk factor for subsequent cigarette smoking in late adolescence and early adulthood. Preliminary evidence from a very small number of studies suggests that marijuana use during...

Many research studies aim to draw causal inferences using data from large, nationally representative survey samples, and many of these studies use propensity score matching to make those causal inferences as rigorous as possible given the non-experimental nature of the data. However, very few applied studies are careful about incorporating the surv...

Among people living with HIV/AIDS (PLHIV), health-related quality of life (HRQOL) is an important clinical metric of perceived well-being. Baseline data from the BEACON study (N = 383) were used to examine relationships between HRQOL and negative social support, HIV-related stigma, viral suppression, and physical and mental health service use among...

Among disadvantaged persons living with HIV/AIDS (PLHIV), patient-provider engagement, which has been defined as patient-provider relationships that promote the use of health care services and are characterized by active listening and supportive decision making, has been associated with antiretroviral therapy (ART) maintenance and viral suppression...

In the presence of treatment effect heterogeneity, the average treatment effect (ATE) in a randomized controlled trial (RCT) may differ from the average effect of the same treatment if applied to a target population of interest. If all treatment effect moderators are observed in the RCT and in a dataset representing the target population, then we c...

Suppose we are interested in the effect of variable $X$ on variable $Y$. If $X$ and $Y$ both influence, or are associated with variables that influence, a common outcome, called a collider, then conditioning on the collider (or on a variable influenced by the collider -- its "child") induces a spurious association between $X$ and $Y$, which is know...

Objectives Participation in the Special Supplemental Nutrition Program for Women, Infants, and Children (WIC) has been associated with lower breastfeeding initiation and duration. This study examines breastfeeding-related factors among WIC participants and nonparticipants that might explain these previous findings. Methods Respondents to the 2007 I...

We developed the first Vietnamese Internalized Homophobia (IH) scale for use with Vietnamese sexual minority women (SMW). Drawing from existing IH scales in the international literature and based on prior qualitative research about SMW in the Viet Nam context, the scale covers two domains: self-stigma (negative attitudes toward oneself as a sexual...

Background: Social cohesion has been shown to be an effective strategy to improve consistent condom use (CCU) and reduce HIV/STI risk among female sex workers (FSW). However, these relationships have not been studied among FSW living with HIV for whom limited interventions have been developed to date. We assessed the association between social cohe...

Background: In 2007 the WHO recommended voluntary male medical circumcision (VMMC) as an important HIV prevention strategy and identified priority countries for VMMC scale up. In spite of VMMC demand creation efforts, Malawi continues to be among the priority countries with the lowest VMMC uptake. This study analyzes the HIV risk profile of men acc...

Purpose: Research linking family rejection and health outcomes in sexual minority people is mostly limited to North America. We assessed the associations between negative treatment by family members and depressive symptoms, life satisfaction, suicidality, and tobacco/alcohol use in sexual minority women (SMW) in Viet Nam. Methods: Data were from...

Chronic pain and substance use can strain the supportive relationships of persons with serious chronic illness, which may increase the likelihood of receiving negative, rather than positive, social support from informal caregivers and social network members. To our knowledge, this is the first study to longitudinally examine the effects of chronic...

We investigate a method to estimate the combined effect of multiple continuous/ordinal mediators on a binary outcome: (a) fit a structural equation model with probit link for the outcome and identity/probit link for continuous/ordinal mediators, (b) predict potential outcome probabilities, and (c) compute natural direct and indirect effects. Step 2...

In a context with limited attention to mental health and prevalent sexual prejudice, valid measurements are a key first step to understanding the psychological suffering of sexual minority populations. We adapted the Patient Health Questionnaire as a depressive symptom severity measure for Vietnamese sexual minority women, ensuring its cultural rel...

Current or former injection drug users with human immunodeficiency virus (HIV) are at high risk for pain, which adversely affects their quality of life and may increase their risk for illicit drug use or relapse. We explored associations between pain symptoms and substance use among injection-drug-using study participants with HIV who had histories...

Objective: To explore the role of informal caregivers in adherence, we compared adherence reports by caregivers to those of care recipients. We identified individual-level and relationship factors associated with agreement between caregivers' reports of recipients' adherence and assessed viral suppression.. Methods: Participants were care recipien...

Background: Few studies have examined the association between having an informal (unpaid) caregiver and viral suppression among persons living with HIV/AIDS (PLHIV) who are on antiretroviral therapy. The current study examined relationships between caregivers’ individual and social network characteristics and care recipient viral suppression. Meth...

People living with HIV/AIDS (PLHIV) have growing rates of morbidity and need for informal care, especially among drug-using PLHIV. Informal caregivers, or persons providing unpaid emotional or instrumental support, have protective effects on the health and well-being of PLHIV. Research suggests that social support, including care recipients' recipr...

Sexual/gender minority persons commonly face rejection from parents and other family members. To date, research on this topic has either measured family rejection as one binary or continuous variable, or characterized family rejection using several variables representing specific behaviors or dimensions of behaviors (a variable-oriented approach)....

With the advent of antiretroviral therapies, persons living with HIV/AIDS (PLHIVs) are living longer but with increased impairment and care needs. The purpose of this study was to assess whether a vulnerable population of PLHIVs preferred informal versus professional care when unable to care for themselves, and individual and support network factor...

Introduction This study assessed to what extent sexual-orientation-related disparities in youth mental health are associated with disproportionate exposure to violence. We evaluated Pearl/VanderWeele’s causally defined direct and indirect effects, extending Muthen’s ordinal-mediator-binary-outcome method to allow multiple mediators. Methods We...

Objective: Low-income African-American, inner-city residents provide disproportionately high levels of informal (unpaid) HIV care (instrumental and emotional support) to family and friends living with HIV/AIDS. We examined evidence of the role of caregivers in care recipients' mental health and associations with their perceived associative stigma r...

Methodological background: A challenge in LGBT health disparities research is lack of comparable LGBT and non-LGBT samples. Even with population samples (preferred over separately recruited LGBT and non-LGBT samples), confounding remains problematic due to small LGBT percentages. Geographical background: No prior research examined LGBT health dispa...