The Gap-Closing Estimand: A Causal Approach to Study Interventions That Close Disparities Across Social Categories

Disparities across race, gender, and class are important targets of descriptive research. But rather than only describe disparities, research would ideally inform interventions to close those gaps. The gap-closing estimand quantifies how much a gap (e.g., incomes by race) would close if we intervened to equalize a treatment (e.g., access to college). Drawing on causal decomposition analyses, this type of research question yields several benefits. First, gap-closing estimands place categories like race in a causal framework without making them play the role of the treatment (which is philosophically fraught for non-manipulable variables). Second, gap-closing estimands empower researchers to study disparities using new statistical and machine learning estimators designed for causal effects. Third, gap-closing estimands can directly inform policy: if we sampled from the population and actually changed treatment assignments, how much could we close gaps in outcomes? I provide open-source software (the R package gapclosing) to support these methods.

Is the STEM gender gap closing?

The Networking for Science Advancement (NSA) team's institutions consist of nine universities located in one large southwestern state. This study evaluated students enrolled from Spring 2017 to Fall 2019 in first- and second-semester general chemistry. Over 90% of the students (n = 6,694) have been exposed to a secondary school isomorphic curriculum. The population studied, Chem I (n = 4,619) and Chem II (n = 2,075), met entry-level criteria and are therefore expected to succeed (i.e., earn grades of A, B or C). This study's focus is to disaggregate data based on binary gender (M/F) in hopes of revealing patterns that might remain hidden when studying an undivided population. In Chem I, the female population was 59.6% and increased to 64.5% for Chem II. The 15-min., diagnostic Math-Up Skills Test’s (MUST) scores identified about half of all students who were unsuccessful (grades of D and F). Results from the study support that males enter Chem I and II with better automaticity skills (what can be done without using a calculator) than females. However, females outperformed males on course averages in Chem I but not Chem II. Our data provide supporting evidence that the gender gap may be closing.

Quantifying the contribution of occupational segregation to racial disparities in health: A gap-closing perspective

Racism causes racial disparities in health, and structural racism has many components. Focusing on one of those components, this paper addresses occupational segregation. I document high onset of work-limiting disabilities in occupations where many workers identify as non-Hispanic Black or as Hispanic. I then pivot to a causal question. Suppose we took a sample from the population and reassigned their occupations to be a function of education alone. To what degree would health disparities narrow for that sample? Using observational data, I estimate that the disparity between non-Hispanic Black and white workers would narrow by one-third. This estimate is credible because of adjustment for lagged measures of demographics, human capital, and health carried out under transparent causal assumptions. The result contributes to understanding about inequality and health by quantifying the contribution of occupational segregation to a disparity: if we took a sample and reassigned occupations, the disparity would narrow but would not disappear. The paper contributes to methodology by illustrating an approach to macro-level claims (how segregation affects a population disparity) that draws on explicitly causal micro-level analyses (potential outcomes for individuals) for which data are abundant.

Pressure-induced ferroelectric-like transition creates a polar metal in defect antiperovskites Hg3Te2X2 (X = Cl, Br)

Ferroelectricity is typically suppressed under hydrostatic compression because the short-range repulsions, which favor the nonpolar phase, increase more rapidly than the long-range interactions, which prefer the ferroelectric phase. Here, based on single-crystal X-ray diffraction and density-functional theory, we provide evidence of a ferroelectric-like transition from phase I213 to R3 induced by pressure in two isostructural defect antiperovskites Hg3Te2Cl2 (15.5 GPa) and Hg3Te2Br2 (17.5 GPa). First-principles calculations show that this transition is attributed to pressure-induced softening of the infrared phonon mode Γ4, similar to the archetypal ferroelectric material BaTiO3 at ambient pressure. Additionally, we observe a gradual band-gap closing from ~2.5 eV to metallic-like state of Hg3Te2Br2 with an unexpectedly stable R3 phase even after semiconductor-to-metal transition. This study demonstrates the possibility of emergence of polar metal under pressure in this class of materials and establishes the possibility of pressure-induced ferroelectric-like transition in perovskite-related systems.