Causal effects of intervening variables in settings with unmeasured confounding

We present new results on average causal effects in settings with unmeasured exposure-outcome confounding. Our results are motivated by a class of estimands, e.g., frequently of interest in medicine and public health, that are currently not targeted by standard approaches for average causal effects. We recognize these estimands as queries about the average causal effect of an intervening variable. We anchor our introduction of these estimands in an investigation of the role of chronic pain and opioid prescription patterns in the opioid epidemic, and illustrate how conventional approaches will lead unreplicable estimates with ambiguous policy implications. We argue that our altenative effects are replicable and have clear policy implications, and furthermore are non-parametrically identified by the classical frontdoor formula. As an independent contribution, we derive a new semiparametric efficient estimator of the frontdoor formula with a uniform sample boundedness guarantee. This property is unique among previously-described estimators in its class, and we demonstrate superior performance in finite-sample settings. Theoretical results are applied with data from the National Health and Nutrition Examination Survey

Changes in US Lifetime Heroin Use and Heroin Use Disorder: Prevalence From the 2001-2002 to 2012-2013 National Epidemiologic Survey on Alcohol and Related Conditions

Importance: Heroin use is an urgent concern in the United States. Little is know about the course of heroin use, heroin use disorder, and associated factors. Objective: To examine changes in the lifetime prevalence, patterns, and associated demographics of heroin use and use disorder from 2001-2002 to 2012-2013 in 2 nationally representative samples of the US adult general population. Design, Setting, and Participants: This survey study included data from 43 093 respondents of the 2001-2002 National Epidemiologic Survey on Alcohol and Related Conditions (NESARC) and 36 309 respondents of the 2012-2013 NESARC-III. Data were analyzed from February 2 to September 15, 2016. Main Outcomes and Measures: Lifetime heroin use and DSM-IV heroin use disorder. Results: Among the 79 402 respondents (43.3% men; 56.7% women; mean [SD] age, 46.1 [17.9] years), prevalence of heroin use and heroin use disorder significantly increased from 2001-2002 to 2012-2013 (use: 0.33% [SE, 0.03%] vs 1.6% [SE, 0.08%]; disorder: 0.21% [SE, 0.03%] vs 0.69% [SE, 0.06%]; P < .001). The increase in the prevalence of heroin use was significantly pronounced among white (0.34% [SE, 0.04%] in 2001-2002 vs 1.90% [SE, 0.12%] in 2012-2013) compared with nonwhite (0.32% [SE, 0.05%] in 2001-2002 vs 1.05% [SE, 0.10%] in 2012-2013; P < .001) individuals. The increase in the prevalence of heroin use disorder was more pronounced among white individuals (0.19% [SE, 0.03%] in 2001-2002 vs 0.82% [SE, 0.08%] in 2012-2013; P < .001) and those aged 18 to 29 (0.21% [SE, 0.06%] in 2001-2002 vs 1.0% [0.17%] in 2012-2013; P = .01) and 30 to 44 (0.20% [SE, 0.04%] in 2001-2002 vs 0.77% [0.10%] in 2012-2013; P = .03) years than among nonwhite individuals (0.25% [SE, 0.04%] in 2001-2002 vs 0.43% [0.07%] in 2012-2013) and older adults (0.22% [SE, 0.04%] in 2001-2002 vs 0.51% [SE, 0.07%] in 2012-2013). Among users, significant differences were found across time in the proportion of respondents meeting DSM-IV heroin use disorder criteria (63.35% [SE, 4.79%] in 2001-2001 vs 42.69% [SE, 2.87%] in 2012-2013; P < .001). DSM-IV heroin abuse was significantly more prevalent among users in 2001-2002 (37.02% [SE, 4.67%]) than in 2012-2013 (19.19% [SE, 2.34%]; P = .001). DSM-IV heroin dependence among users was similar in 2001-2002 (28.22% [SE, 3.95%]) and in 2012-2013 (25.02% [SE, 2.20%]; P = .48). The proportion of those reporting initiation of nonmedical use of prescription opioids before initiating heroin use increased across time among white individuals (35.83% [SE, 6.03%] in 2001-2002 to 52.83% [SE, 2.88%] in 2012-2013; P = .01). Conclusions and Relevance: The prevalence of heroin use and heroin use disorder increased significantly, with greater increases among white individuals. The nonmedical use of prescription opioids preceding heroin use increased among white individuals, supporting a link between the prescription opioid epidemic and heroin use in this population. Findings highlight the need for educational campaigns regarding harms related to heroin use and the need to expand access to treatment in populations at increased risk for heroin use and heroin use disorder

Optimal regimes for algorithm-assisted human decision-making

We introduce optimal regimes for algorithm-assisted human decision-making. Such regimes are decision functions of measured pre-treatment variables and enjoy a "superoptimality" property whereby they are guaranteed to outperform conventional optimal regimes currently considered in the literature. A key feature of these superoptimal regimes is the use of natural treatment values as input to the decision function. Importantly, identification of the superoptimal regime and its value require exactly the same assumptions as identification of conventional optimal regimes in several common settings, including instrumental variable settings. As an illustration, we study superoptimal regimes in an example that has been presented in the optimal regimes literature

A Graphical Description of Partial Exchangeability

Partial exchangeability is sufficient for the identification of some causal effects of interest. Here we review the use of common graphical tools and the sufficient component cause model in the context of partial exchangeability. We illustrate the utility of single world intervention graphs (SWIGs) in depicting partial exchangeability and provide an illustrative example of when partial exchangeability might hold in the absence of complete exchangeability

Associations of intimate partner violence and financial adversity with familial homelessness in pregnant and postpartum women: A 7-year prospective study of the ALSPAC cohort.

ObjectiveTo determine whether emotional and physical intimate partner violence (IPV) and financial adversity increase risk of incident homelessness in pregnancy and the post-partum period.Study designData were drawn from the Avon Longitudinal Study of Parents and Children, which starting in 1990 mailed questionnaires to 14,735 mothers in the UK, over 7 years from pregnancy onwards. Marginal structural models and multiple imputation were used to address time-varying confounding of the primary variables, testing for interaction between concurrent emotional/physical IPV and financial adversity, and adjusted for baseline age, ethnicity, education, partner's alcohol use, parity, depression, and social class.ResultsEmotional IPV (HR 1.44 (1.13,1.84)), physical IPV (HR 2.05 (1.21,3.49)), and financial adversity (HR 1.59 (1.44,1.77)) each predicted a multiplicative increase in the discrete-time hazard of incident homelessness. We identified joint effects for concurrent emotional IPV and financial adversity (HR 2.09 (1.35,3.22)) and concurrent physical IPV and financial adversity (HR 2.79 (1.21,6.44)). We further identified a temporary decline in self-reported physical IPV among mothers during pregnancy and up to 8 months post-partum.ConclusionsEmotional and physical IPV and financial adversity independently and jointly increase the risk of incident homelessness. The effects of emotional and physical IPV are comparable to or greater than the risk of financial adversity. Homelessness prevention policies should consider IPV victims as high-risk, regardless of financial status. Furthermore, self-reported physical IPV declines temporarily during pregnancy and up to 8 months post-partum. Screening for IPV in this period may miss high-risk individuals

Causal inference with limited resources: proportionally-representative interventions

Investigators often evaluate treatment effects by considering settings in which all individuals are assigned a treatment of interest, assuming that an unlimited number of treatment units are available. However, many real-life treatments are of limited supply and cannot be provided to all individuals in the population. For example, patients on the liver transplant waiting list cannot be assigned a liver transplant immediately at the time they reach highest priority because a suitable organ is not likely to be immediately available. In these cases, investigators may still be interested in the effects of treatment strategies in which a finite number of organs are available at a given time, that is, treatment regimes that satisfy resource constraints. Here, we describe an estimand that can be used to define causal effects of treatment strategies that satisfy resource constraints: proportionally-representative interventions for limited resources. We derive a simple class of inverse probability weighted estimators, and apply one such estimator to evaluate the effect of restricting or expanding utilization of "increased risk" liver organs to treat patients with end-stage liver disease. Our method is designed to evaluate policy-relevant interventions in the setting of finite treatment resources

The widening gender gap in marijuana use prevalence in the U.S. during a period of economic change, 2002–2014

Aim: Concurrently with increasingly permissive attitudes towards marijuana use and its legalization, the prevalence of marijuana use has increased in recent years in the U.S. Substance use is generally more prevalent in men than women, although for alcohol, the gender gap is narrowing. However, information is lacking on whether time trends in marijuana use differ by gender, or whether socioeconomic status in the context of the Great Recession may affect these changes. Methods: Using repeated cross-sectional data from the National Survey on Drug Use and Health (2002–2014), we examined changes over time in prevalence of past-year marijuana use by gender, and whether gender differences varied across income levels. After empirically determining a change point in use in 2007, we used logistic regression to test interaction terms including time, gender, and income level. Results: Prevalence of marijuana use increased for both men (+4.0%) and women (+2.7%) from 2002 to 2014, with all of the increase occurring from 2007 to 2014. Increases were greater for men, leading to a widening of the gender gap over time (p < 0.001). This divergence occurred primarily due to increased prevalence among men in the lowest income level (+6.2%) from 2007 to 2014. Conclusion: Our findings are consistent with other studies documenting increased substance use during times of economic insecurity, especially among men. Corresponding with the Great Recession and lower employment rate beginning in 2007, low-income men showed the greatest increases in marijuana use during this period, leading to a widening of the gender gap in prevalence of marijuana use over time

Sexual assault incidents among college undergraduates: Prevalence and factors associated with risk.

Sexual assault on college campuses is a public health issue. However varying research methodologies (e.g., different sexual assault definitions, measures, assessment timeframes) and low response rates hamper efforts to define the scope of the problem. To illuminate the complexity of campus sexual assault, we collected survey data from a large population-based random sample of undergraduate students from Columbia University and Barnard College in New York City, using evidence based methods to maximize response rates and sample representativeness, and behaviorally specific measures of sexual assault to accurately capture victimization rates. This paper focuses on student experiences of different types of sexual assault victimization, as well as sociodemographic, social, and risk environment correlates. Descriptive statistics, chi-square tests, and logistic regression were used to estimate prevalences and test associations. Since college entry, 22% of students reported experiencing at least one incident of sexual assault (defined as sexualized touching, attempted penetration [oral, anal, vaginal, other], or completed penetration). Women and gender nonconforming students reported the highest rates (28% and 38%, respectively), although men also reported sexual assault (12.5%). Across types of assault and gender groups, incapacitation due to alcohol and drug use and/or other factors was the perpetration method reported most frequently (> 50%); physical force (particularly for completed penetration in women) and verbal coercion were also commonly reported. Factors associated with increased risk for sexual assault included non-heterosexual identity, difficulty paying for basic necessities, fraternity/sorority membership, participation in more casual sexual encounters ("hook ups") vs. exclusive/monogamous or no sexual relationships, binge drinking, and experiencing sexual assault before college. High rates of re-victimization during college were reported across gender groups. Our study is consistent with prevalence findings previously reported. Variation in types of assault and methods of perpetration experienced across gender groups highlight the need to develop prevention strategies tailored to specific risk groups