Sensitivity Analysis for Unmeasured Confounding in Meta-Analyses

Random-effects meta-analyses of observational studies can produce biased estimates if the synthesized studies are subject to unmeasured confounding. We propose sensitivity analyses quantifying the extent to which unmeasured confounding of specified magnitude could reduce to below a certain threshold the proportion of true effect sizes that are scientifically meaningful. We also develop converse methods to estimate the strength of confounding capable of reducing the proportion of scientifically meaningful true effects to below a chosen threshold. These methods apply when a "bias factor" is assumed to be normally distributed across studies or is assessed across a range of fixed values. Our estimators are derived using recently proposed sharp bounds on confounding bias within a single study that do not make assumptions regarding the unmeasured confounders themselves or the functional form of their relationships to the exposure and outcome of interest. We provide an R package, ConfoundedMeta, and a freely available online graphical user interface that compute point estimates and inference and produce plots for conducting such sensitivity analyses. These methods facilitate principled use of random-effects meta-analyses of observational studies to assess the strength of causal evidence for a hypothesis

The Anisoplanatic Point Spread Function in Adaptive Optics

The effects of anisoplanatism on the adaptive optics point spread function are investigated. A model is derived that combines observations of the guide star with an analytic formulation of anisoplanatism to generate predictions for the adaptive optics point spread function at arbitrary locations within the field of view. The analytic formulation captures the dependencies of anisoplanatism on aperture diameter, observing wavelength, angular offset, zenith angle and turbulence profile. The predictions of this model are compared to narrowband 2.12 um and 1.65 um images of a 21 arcsec binary (mV=7.3, 7.6) acquired with the Palomar Adaptive Optics System on the Hale 5 meter telescope. Contemporaneous measurements of the turbulence profile made with a DIMM/MASS unit are used together with images of the primary to predict the point spread function of the binary companion. Predicted companion Strehl ratios are shown to match measurements to within a few percent, whereas predictions based on the isoplanatic angle approximation are highly discrepant. The predicted companion point spread functions are shown to agree with observations to 10%. These predictions are used to measure the differential photometry between binary members to an accuracy of 1 part in 10^{3}, and the differential astrometry to an accuracy of 1 mas. Errors in the differential astrometry are shown to be dominated by differential atmospheric tilt jitter. These results are compared to other techniques that have been employed for photometry, astrometry, and high contrast imaging.Comment: 26 pages, 7 figure

Development of a systems-level design language

This project will result in design tools and technologies that will facilitate the creation of complex, heterogeneous systems that meet requirements. From a more pure-research perspective, this project will also lay the foundation for further work into modeling language development and the application of verification and validation techniques to system design

Analytic Scattering and Refraction Models for Exoplanet Transit Spectra

Observations of exoplanet transit spectra are essential to understanding the physics and chemistry of distant worlds. The effects of opacity sources and many physical processes combine to set the shape of a transit spectrum. Two such key processes - refraction and cloud and/or haze forward scattering - have seen substantial recent study. However, models of these processes are typically complex, which prevents their incorporation into observational analyses and standard transit spectrum tools. In this work, we develop analytic expressions that allow for the efficient parameterization of forward scattering and refraction effects in transit spectra. We derive an effective slant optical depth that includes a correction for forward scattered light, and present an analytic form of this correction. We validate our correction against a full-physics transit spectrum model that includes scattering, and we explore the extent to which the omission of forward scattering effects may bias models. Also, we verify a common analytic expression for the location of a refractive boundary, which we express in terms of the maximum pressure probed in a transit spectrum. This expression is designed to be easily incorporated into existing tools, and we discuss how the detection of a refractive boundary could help indicate the background atmospheric composition by constraining the bulk refractivity of the atmosphere. Finally, we show that opacity from Rayleigh scattering and collision induced absorption will outweigh the effects of refraction for Jupiter-like atmospheres whose equilibrium temperatures are above 400-500 K.Comment: ApJ accepted; submitted Feb. 7, 201

Hadron Collider Sensitivity to Fat Flavourful Z′Z^\primes for RK(∗)R_{K^{(\ast)}}

We further investigate the case where new physics in the form of a massive $Z^\prime$ particle explains apparent measurements of lepton flavour non-universality in $B \rightarrow K^{(\ast)} l^+ l^-$ decays. Hadron collider sensitivities for direct production of such $Z^\prime$s have been previously studied in the narrow width limit for a $\mu^+ \mu^-$ final state. Here, we extend the analysis to sizeable decay widths and improve the sensitivity estimate for the narrow width case. We estimate the sensitivities of the high luminosity 14 TeV Large Hadron Collider (HL-LHC), a high energy 27 TeV LHC (HE-LHC), as well as a potential 100 TeV future circular collider (FCC). The HL-LHC has sensitivity to narrow $Z^\prime$ resonances consistent with the anomalies. In one of our simplified models the FCC could probe 23 TeV $Z^\prime$ particles with widths of up to 0.35 of their mass at 95\% confidence level (CL). In another model, the HL-LHC and HE-LHC cover sizeable portions of parameter space, but the whole of perturbative parameter space can be covered by the FCC.Comment: 24 pages, 11 figures; v2 Reference

Development of a systems-level design language

This project will result in design tools and technologies that will facilitate the creation of complex, heterogeneous systems that meet requirements. From a more pure-research perspective, this project will also lay the foundation for further work into modeling language development and the application of verification and validation techniques to system design

Development and validation of a new glaucoma screening test using temporally modulated flicker

Purpose Describing the psychometric characteristics and diagnostic accuracy of the Accelerator 4‐Alternative Forced‐Choice Flicker Test prototype (A4FTp) for detecting chronic open angle glaucoma (COAG). Methods A4FTp measures temporally‐modulated flicker thresholds in regions of the visual field with high susceptibility to glaucomatous loss. We initially evaluated its psychometric properties on 20 normals (aged 33.8 ± 8.5 years) who were tested multiple times over a period of 3 months. All subjects underwent four repetitions for shorter (T8) and longer (T12) staircase termination criteria, to determine the most suitable threshold criterion. Four randomly selected subjects underwent a total of 10 repetitions to study test‐retest repeatability and learning effects. To determine its diagnostic accuracy, one eye of 40 participants with COAG and 38 normal controls were tested with the A4FTp in comparison with the Frequency Doubling Technology (FDT; C20‐5 programme) and iVue Spectral Domain Optical Coherence Tomography (SD‐OCT). Tests were conducted in a random order with results masked to the clinician conducting the reference ophthalmic examination. The accuracy of each test was determined by analysis of the area under the receiver operator characteristic curve (AUROC). Results A4FTp flicker thresholds were stable, with standard deviations of only 0.52 decilog (dL) for T8, increasing to 1.32 dL for T12, and no significant flicker sensitivity threshold improvement over the 10 repeat runs. T8 was superior to T12 on several other measures, so it was used for the remaining comparisons. In terms of diagnostic accuracy, the mean AUROC for the three tests were A4FTp [T8 criterion; 0.82, 95% confidence interval (0.73–0.92)]; SD‐OCT [any RNFL parameter p < 1% level; 0.90 (0.83–0.97)]; and FDT [one or more locations missed at p < 5% level; 0.91 (0.82–0.96)]. There was no statistical difference in AUROC between A4FTp and SD‐OCT (p = 0.18) or FDT (p = 0.12). The A4FTp test duration averaged just over 2 min per eye, taking approximately one‐third of the time for completion of the HFA SITA 24‐2 algorithm (conducted as part of the reference examination) and twice the time for the suprathreshold FDT. Conclusion Test accuracy for the A4FTp was comparable to those of the FDT and SD‐OCT for the detection of COAG. Time taken to complete the A4FTp was relatively short and initial results are promising. With further refinement, the A4FTp could have a future role in glaucoma detection

Who Benefits from Obtaining a GED? Evidence from High School and Beyond

This paper examines the value of the GED credential and the conventional high school diploma in explaining the earnings of 27-year-old males in the early 1990s. The data base is the High School & Beyond sophomore cohort. We replicate the basic findings of prior studies that implicitly assume the labor market value of the GED credential does not depend on the skills with which dropouts left school. We show that these average effects mask a more complicated pattern. Obtaining a GED is associated with higher earnings at age 27 for those male dropouts who had very weak cognitive skills as tenth graders, but not for those who had stronger cognitive skills as tenth graders.